Science Questions

11th Std Science Lesson Wise Questions in English – Part 2

September 15, 2022

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11th Science Lesson 5 Questions in English

5] Gravitation

1. Which of these 17^th century theory explained the motion of celestial and terrestrial objects?

a) Atomic Theory

b) Theory of Gravitation

c) Theory of Relativity

d) Quantum Theory

Explanation

The ‘Theory of Gravitation’ was developed by Newton in the late 17^thcentury to explain the motion of celestial objects and terrestrial objects and answer most of the queries raised. In spite of the study of gravitation and its effect on celestial objects, spanning last three centuries, “gravitation” is still one of the active areas of research in physics today.

2. For which of this discovery Albert Einstein was awarded Nobel Prize in 2017?

a) Gravitational Waves

b) Plank’s constant

c) Earth distance from the Sun

d) Solar system

Explanation

In 2017, the Nobel Prize in Physics was given for the detection of ‘Gravitational waves’ which was theoretically predicted by Albert Einstein in the year 1915.

3. Who was the first person to explain the geocentric model?

a) Aristotle

b) Claudius Ptolemy

c) Copernicus

d) Albert Einstein

Explanation

In the second century, Claudius Ptolemy, a famous Greco-Roman astronomer, developed a theory to explain the motion of celestial objects like the Sun, the Moon, Mars, and Jupiter etc. This theory was called the geocentric model.

4. Choose the correct statements.

i) The Earth is at the centre of the universe and all celestial objects orbit the earth except the Sun in the geocentric model.

ii) Ptolemy’s model does not match with the naked eye observations of Sky.

iii) Ptolemy’s model did not explain the motion of Mars and Jupiter effectively.

a) i only

b) ii only

c) iii only

d) All the above

Explanation

According to the geocentric model, the Earth is at the centre of the universe and all celestial objects including the Sun, the Moon, and other planets orbit the Earth. Ptolemy’s model closely matched with the observations of the sky with our naked eye. But later, astronomers found that even though Ptolemy’s model successfully explained the motion of the Sun and the Moon up to a certain level, the motion of Mars and Jupiter could not be explained effectively.

5. In which century Nicholas Copernicus proposed the heliocentric model?

a) 2^nd century

b) 15^th century

c) 20^th century

d) 17^th century

Explanation

In the 15th century, a Polish astronomer, Nicholas Copernicus (1473-1543) proposed a new model called the ‘Heliocentric model’.

6. Which of the following is not correct regarding the heliocentric model?

a) The Nicholas Copernicus proposed the heliocentric model was an American astronomer.

b) The Sun was considered to be at the centre of the solar system.

c) All the planets orbited the Sun in circular orbits.

d) Heliocentric model explained the motion of all celestial objects.

Explanation

A Polish astronomer, Nicholas Copernicus (1473-1543) proposed a new model heliocentric model. In the ‘Heliocentric model’ the Sun was considered to be at the centre of the solar system and all planets including the Earth orbited the Sun in circular orbits. This model successfully explained the motion of all celestial objects.

7. Who discovered that all objects are accelerated towards the Earth?

a) Tycho

b) Copernicus

c) Galileo

d) Kepler

Explanation

Around the same time, Galileo, a famous Italian physicist discovered that all objects close to Earth were accelerated towards the Earth at the same rate.

8. Whose observations were used to form the Kepler’s law of planetary motion?

a) Tycho Brahe

b) Johannes Kepler

c) Albert Einstein

d) Nicholas Copernicus

Explanation

A noble man called Tycho Brahe (1546-1601) spent his entire lifetime in recording the observations of the stellar and planetary positions with his naked eye. The data that he compiled were analysed later by his assistant Johannes Kepler (1571–1630) and eventually the analysis led to the deduction of the laws of the planetary motion. These laws are termed as ‘Kepler’s laws of planetary motion’.

9. Which of these statements are not true regarding the Kepler’s law of Orbits?

i) All the planets move around the Sun in an elliptical orbit.

ii) The Closest point of approach of the planet to the Sun foci is called as perihelion.

iii) Copernicus and Ptolemy considered the planets orbits to be elliptical around the Sun.

a) i only

b) ii only

c) iii only

d) None of the above

Explanation

Kepler’s laws are stated as follows: Law of orbits: Each planet moves around the Sun in an elliptical orbit with the Sun at one of the foci. The closest point of approach of the planet to the Sun ‘P’ is called perihelion and the farthest point ‘A’ is called aphelion. The semi-major axis is ‘a’ and semi-minor axis is ‘b’. In fact, both Copernicus and Ptolemy considered planetary orbits to be circular, but Kepler discovered that the actual orbits of the planets are elliptical.

10. Assertion (A): The Planets travel at varying speeds around the Sun to cover equal area in equal intervals of time.

Reasoning(R): The Sun is not at the centre of ellipse so the planets travel faster near the sun and slower when they are farther.

a) Both A and R is True and R is the correct explanation of A.

b) Both A and R is True but R is not the correct explanation of A.

c) A is True but R is False.

d) Both A and R is False.

Explanation

The radial vector (line joining the Sun to a planet) sweeps equal areas in equal intervals of time. The white shaded portion is the area DA swept in a small interval of time Dt, by a planet around the Sun. Since the Sun is not at the centre of the ellipse, the planets travel faster when they are nearer to the Sun and slower when they are farther from it, to cover equal area in equal intervals of time. Kepler discovered the law of area by carefully noting the variation in the speed of planets.

11. Which of the following statement is not correct regarding the time period of revolution of a planet around the sun?

a) The square of the revolution time is directly proportional to the cube of semi-major axis of the ellipse.

b) The Planets revolve around the elliptical orbit of the Sun.

c) The distance of the planet from the Sun and the time period of revolution vary at the same rate.

d) The Distance of the planet from the Sun increases and the revolution time period decreases.

Explanation

The square of the time period of revolution of a planet around the Sun in its elliptical orbit is directly proportional to the cube of the semi-major axis of the ellipse. It can be written as: where, T is the time period of revolution for a planet and a is the semi-major axis. Physically this law implies that as the distance of the planet from the Sun increases, the time period also increases but not at the same rate.

12. State the constant value relating Kepler’s third law.

a) T⁵/ a⁴

b) T²/ a³

c) T³/ a⁵

d) T²/ a

Explanation

The time period of revolution of planets around the Sun along with their semi-major axes are given. We can realize that T²/ a³ are nearly a constant endorsing Kepler’s third law.

13. Which of the planet takes around 165 years around the Sun?

a) Mars

b) Neptune

c) Uranus

d) Jupiter

14. Identify the Incorrect Match of the Planet and the revolution time around the sun.

A. Venus i) 0.615yrs

B. Jupiter ii) 29.55yrs

C. Uranus iii) 84yrs

D. Mars iv) 1.88yrs

a) i only

b) ii only

c) iii only

d) iv only

15. Which of the following planets have the highest semi-major axis?

a) Earth

b) Saturn

c) Venus

d) Uranus

Explanation

The time period of revolution of the planets revolving around the Sun and their semi-major axes.

16. Which of these laws endorse the value of the T²/ a³ as constant?

a) Kepler’s third law

b) Newton theory

c) Gravitational theory

d) None of the above

Explanation

The time period of revolution of planets around the Sun along with their semi-major axes are given. we can realize that T²/ a³ is nearly a constant endorsing Kepler’s third law.

17. Which of the following person analysed the Kepler’s law?

a) Galileo

b) Isaac Newton

c) Albert Einstein

d) Copernicus

Explanation

Even though Kepler’s laws were able to explain the planetary motion, they failed to explain the forces responsible for it. It was Isaac Newton who analysed Kepler’s laws, Galileo’s observations and deduced the law of gravitation.

18. Choose the Incorrect statements.

i) Newton’s law of gravitation states that any particle is attracted by other particle with an attractive force.

ii) The strength of the attraction force is directly proportional to the product of the masses.

iii) The Square of the distance between the particles is also directly varies proportional to the force of attraction.

a) i only

b) ii only

c) iii only

d) None of the above

Explanation

Newton’s law of gravitation states that a particle of mass M1 attracts any other particle of mass M2 in the universe with an attractive force. The strength of this force of attraction was found to be directly proportional to the product of their masses and is inversely proportional to the square of the distance between them.

19. What is the value of the gravitational constant?

a) 6.67 x 10 ^-10Nm²kg

b) 6.67 x 10 ^-11Nm²kg^-2

c) 6.67 x 10 ¹⁷Nmkg^-2

d) 6.67 x 10 ^-15Nm²kg^-2

Explanation

G is the Gravitational constant that has the value of 6.67 x 10 ^-11Nm²kg^-2

20. Which of this planet may experience less gravitational force from the sun?

a) Earth

b) Jupiter

c) Mercury

d) Mars

Explanation

As the distance between two masses increases, the strength of the force tends to decrease because of inverse dependence on r2. Physically it implies that the planet Uranus experiences less gravitational force from the Sun than the Earth since Uranus is at larger distance from the Sun compared to the Earth.

21. Assertion (A): The reaction force is exerted by the Earth on the Sun is directed towards the Earth.

Reasoning(R): The gravitational forces between two particles always constitute an action-reaction pair.

a) Both A and R is True and R is the correct explanation of A.

b) Both A and R is True but R is not the correct explanation of A.

c) A is True but R is False.

d) Both A and R is False.

Explanation

The gravitational forces between two particles always constitute an action- reaction pair. It implies that the gravitational force exerted by the Sun on the Earth is always towards the Sun. The reaction-force is exerted by the Earth on the Sun. The direction of this reaction force is towards Earth.

22. Choose the Incorrect statements.

i) The Earth’s angular momentum about the Sun is constant throughout the motion.

ii) The torque experienced by the Earth due to gravitational force of the Sun is a constant scalar.

a) i only

b) ii only

c) Both i and ii

d) None of the above

Explanation

The torque experienced by the Earth due to the gravitational force of the Sun is given by L is a constant vector. The angular momentum of the Earth about the Sun is constant throughout the motion. It is true for all the planets. In fact, this constancy of angular momentum leads to the Kepler’s second law.

23. Which of these assumptions is made to calculate the force between the Sun and the Earth?

a) Earth and the Sun are point masses.

b) The mass of Earth is zero.

c) Mass of the Sun is infinity.

d) All the above

Explanation

When it is said that Earth orbits around the Sun due to Sun’s gravitational force, we assumed Earth and Sun to be point masses. This assumption is a good approximation because the distance between the two bodies is very much larger than their diameters. For some irregular and extended objects separated by a small distance, we cannot directly use the equation. Instead, we have to invoke separate mathematical treatment which will be brought forth in higher classes.

24. State the Newton’s equation for the centripetal acceleration towards centre for the circular orbit?

a) a = v³

b) a = – v²/ r

c) a = v / r²

d) a = v r

Explanation

Newton considered the orbits of the planets as circular. For circular orbit of radius r, the centripetal acceleration towards the centre is ,

Here v is the velocity and r, the distance of the planet from the center of the orbit.

25. Assertion (A): The shape of orbits of the planet around the Sun is elliptical.

Reasoning(R): The Planets orbit is very close to being circular as it has small deviation from the circular shape.

a) Both A and R is True and R is the correct explanation of A.

b) Both A and R is True but R is not the correct explanation of A.

c) A is True but R is False.

d) Both A and R is False.

Explanation

We assumed that the orbit of the planet to be circular which is not true as the orbit of the planet around the Sun is elliptical. But this circular orbit assumption is justifiable because planet’s orbit is very close to being circular and there is only a very small deviation from the circular shape.

26. Who measured the distance between the Earth and the Moon?

a) Hipparchrus

b) Eratosthenes

c) Copernicus

d) Kepler

Explanation

The radius of the Earth was measured by Greek librarian Eratosthenes and distance between the Earth and the Moon was measured by Greek astronomer Hipparchrus 2400 years ago.

27. Assertion (A): The Value of gravitational constant plays an important role in the law of gravitation.

Reasoning(R): The Value of G explains the gravitational force between the Earth and the Sun is so great and between small objects is negligible.

a) Both A and R is True and R is the correct explanation of A.

b) Both A and R is True but R is not the correct explanation of A.

c) A is True but R is False.

d) Both A and R is False.

Explanation

In the law of gravitation, the value of gravitational constant G plays a very important role. The value of G explains why the gravitational force between the Earth and the Sun is so great while the same force between two small objects (for example between two human beings) is negligible.

28. Who discovered the experimental value of the gravitational constant?

a) Kepler

b) Henry Cavendish

c) Copernicus

d) Isaac Newton

Explanation

In the year 1798, Henry Cavendish experimentally determined the value of gravitational constant ‘G’ by using a torsion balance. He calculated the value of ‘G’ to be equal to 6.75 ×10 ^-11Nm² kg^-2.

29. What is the exact accepted value of the gravitational constant?

a) 66.672 × 10^-11 Nmkg^-2

b) 6.67259 ×10^-11 Nm²kg^-2

c) 6.67259 x 10⁵

d) 12.663 ×10^-11 Nm²kg^-2.

Explanation

Using modern techniques a more accurate value of G could be measured. The currently accepted value of G is 6.67259 ×10^-11 Nm²kg^-2.

30. Based on which property the forces are classified?

a) Type of interaction

b) Movement of object

c) Type of objects

d) Number of forces involved

Explanation

Force is basically due to the interaction between two particles. Depending upon the type of interaction we can have two kinds of forces: Contact forces and Non-contact forces.

31. Assertion (A): Contact forces are applied to object in physical contact with the other object.

Reasoning(R): The movement of the object is caused by the physical force exerted through the contact.

a) Both A and R is True and R is the correct explanation of A.

b) Both A and R is True but R is not the correct explanation of A.

c) A is True but R is False.

d) Both A and R is False.

Explanation

Contact forces are the forces applied where one object is in physical contact with the other. The movement of the object is caused by the physical force exerted through the contact between the object and the agent which exerts force.

32. Assertion (A): The magnitude of E decreases as the distance increases.

Reasoning(R): The strength of gravitational field decreases as we move away from the mass.

a) Both A and R is True and R is the correct explanation of A.

b) Both A and R is True but R is not the correct explanation of A.

c) A is True but R is False.

d) Both A and R is False.

Explanation

The strength of the gravitational field decreases as we move away from the mass M as depicted. The magnitude of E decreases as the distance r increases.

33. Which of this physical quantity carries energy and momentum in space?

a) Field

b) Space

c) Charge

d) Quantum

Explanation

The “field” concept was introduced as a mathematical tool to calculate gravitational interaction. Later it was found that field is a real physical quantity and it carries energy and momentum in space. The concept of field is inevitable in understanding the behaviour of charges.

34. Which of the following has the unit Newton per kilogram?

a) Gravity

b) Gravitational field

c) Gravitational intensity

d) Gravity constant

Explanation

The unit of gravitational field is Newton per kilogram (N/kg) or m s^-2.

35. Choose the correct statements.

i) The superposition principle of gravitational fields involves the vector sum of the entire gravitational field due to individual masses.

ii) The total gravitational field at a point is irrespective of all the individual masses.

a) i only

b) ii only

c) Both i and ii

d) Neither i nor ii

Explanation

Consider ‘n’ particles of masses m_1,m _2,…m_n distributed in space at position r_1,r_2,…r_n with respect to point P. The total gravitational field at a point P due to all the masses is given by the vector sum of the gravitational field due to the individual masses. This principle is known as superposition of gravitational fields.

36. Assertion (A): The gravitational potential energy is always a negative value.

Reasoning(R): The system does the work when two masses come together from infinity.

a) Both A and R is True and R is the correct explanation of A.

b) Both A and R is True but R is not the correct explanation of A.

c) A is True but R is False.

d) Both A and R is False.

Explanation

The gravitational potential energy Ur ‑ is always negative because when two masses come together slowly from infinity, work is done by the system.

37. Choose the correct statements.

i) The unit of gravitational potential energy is Joule / s which are a vector quantity.

ii) The gravitational potential energy depends on the masses and the distance between the masses.

a) i only

b) ii only

c) Both i and ii

d) Neither i nor ii

Explanation

The unit of gravitational potential energy Ur ‑ is Joule and it is a scalar quantity. The gravitational potential energy depends upon the two masses and the distance between them.

38. State the gravitational potential energy of a system with two masses m1 and m2 and the distance between that is r.

a) – G m₁m₂/r

b) G m₁m₂ + r

c) G m₁m₂r

d) G m₁m₂/ r²

Explanation

We can define gravitational potential energy of a system of two masses m1 and m2 separated by a distance r as the amount of work done to take the mass m2 from a distance r to infinity assuming m1 to be fixed in its position and is written as,

39. Which of the following value is responsible for the gravitational field?

a) Number of source

b) Forces

c) Source mass

d) Distance between the objects

Explanation

The gravitational field E depends only on the source mass which creates the field. It is a vector quantity. We can also define a scalar quantity called “gravitational potential” which depends only on the source mass.

40. What is the unit of the gravitational potential?

a) J s

b) J kg^-1

c) J / s

d) J

Explanation

The gravitational potential at distance r is equivalent to gravitational potential energy per unit mass at the same distance r. It is a scalar quantity and its unit is J kg^-1.

41. Choose the Incorrect statements.

i) The Gravitational field and gravitational force are vector quantities.

ii) The gravitational potential and gravitational potential energy are scalar quantities.

iii) The Vector quantities are used for easy analyses of the motion of particles.

a) i only

b) ii only

c) iii only

d) None of the above

Explanation

Gravitational field and gravitational force are vector quantities whereas the gravitational potential and gravitational potential energy are scalar quantities. The motion of particles can be easily analysed using scalar quantities than vector quantities.

42. Assertion (A): The gravitation pull produces a constant acceleration in all the bodies near the Earth’s surface.

Reasoning(R): Newton’s second law states that an object is accelerated only under the action of a force.

a) Both A and R is True and R is the correct explanation of A.

b) Both A and R is True but R is not the correct explanation of A.

c) A is True but R is False.

d) Both A and R is False.

Explanation

When objects fall on the Earth, the acceleration of the object is towards the Earth. From Newton’s second law, an object is accelerated only under the action of a force. In the case of Earth, this force is the gravitational pull of Earth. This force produces a constant acceleration near the Earth’s surface in all bodies, irrespective of their masses.

43. Which of this value does not depend on the gravitational force exerted by earth near its surface?

a) Mass of the Earth

b) Radius of the Earth

c) Distance between the object and the Earth

d) Mass of the object

Explanation

The gravitational force exerted by Earth on the mass m near the surface of the Earth is given by,

M_E– mass of the Earth, m-mass of the object, R_E– radius of the Earth.

44. What is the magnitude of the earth’s gravity?

a) G M_e / R_e²

b) G M_e³ / R_e³

c) G M_e² / R_e

d) G M_e / R_e

Explanation

The acceleration experienced by the object near the surface of the Earth due to its gravity is called acceleration due to gravity. It is denoted by the symbol g. The magnitude of acceleration due to gravity is g,

45. Which of this factor does not depend on the mass of an object?

a) Acceleration due to gravity

b) Kinetic energy

c) Frictional forces

d) All the above

Explanation

It is to be noted that the acceleration experienced by any object is independent of its mass. The value of g depends only on the mass and radius of the Earth. In fact Galileo arrived at the same conclusion 400 years ago that all objects fall towards the Earth with the same acceleration through various quantitative experiments.

46. What is the value of the acceleration due to gravity near Earth equator?

a) 19.8 m s

b) 12.8 ms^-2

c) 9.8 m s^-2

d) 6.6 m

Explanation

The acceleration due to gravity g is found to be 9.8 m s^-2 on the surface of the Earth near the equator.

47. Choose the correct statements.

i) The Earth’s centrifugal force depends on the revolution time.

ii) The objects on earth’s surface experiences only the centrifugal force of earth’s spinning.

iii) The centrifugal force on objects on the surface of the Earth depends on the latitude of the object.

a) i only

b) ii only

c) iii only

d) All the above

Explanation

Whenever we analyse the motion of objects in rotating frames we must take into account the centrifugal force. Even though we treat the Earth as an inertial frame, it is not exactly correct because the Earth spins about its own axis. So when an object is on the surface of the Earth, it experiences a centrifugal force that depends on the latitude of the object on Earth. If the Earth were not spinning, the force on the object would have been mg. However, the object experiences an additional centrifugal force due to spinning of the Earth.

48. Which of this value is represented by the symbol λ in the centrifugal force of an object?

a) Wavelength

b) Latitude

c) Mass

d) Length

Explanation

This centrifugal force is given by mω²R‘. R’ = R cos λ where λ is the latitude. The component of centrifugal acceleration experienced by the object in the direction opposite to g.

49. At which of the following places the acceleration due to gravity is minimum?

a) North Pole

b) Earth’s atmosphere

c) South Pole

d) Equator

Explanation

From the above equation of we can infer that at equator, λ= 0; g’= ‑ g- ω²R. The acceleration due to gravity is minimum. At poles λ= 90; g’ = g, it is maximum. At the equator, g’ is minimum.

50. Which of the following is mainly found in earth’s atmosphere?

a) Oxygen

b) Hydrogen

c) Helium

d) Argon

Explanation

Hydrogen and helium are the most abundant elements in the universe but Earth’s atmosphere consists mainly of nitrogen and oxygen.

51. Which of these molecules easily escape from the earth surface?

a) Nitrogen

b) Hydrogen

c) Helium

d) Carbon dioxide

Explanation

Lighter molecules such as hydrogen and helium have enough speed to escape from the Earth unlike the heavier ones such as nitrogen and oxygen. The average speed of hydrogen and helium atoms compared with the escape speed of the Earth is presented in the kinetic theory of gases.

52. What is the value of the distance covered by the satellite during one rotation in the orbit?

a) R_Eh

b) 2πR_Eh

c) 2πR

d) 2R_E

Explanation

Time period of the satellite: The distance covered by the satellite during one rotation in its orbit is equal to 2πR_Ehand time taken for it is the time period, T. Then Speed v Distance travelled Time taken

53. What is the value of the total energy of a satellite orbiting the earth?

a) Kinetic energy of the Satellite

b) Gravitational potential energy

c) Earth’s Magnetic energy

d) Both a and b

Explanation

The total energy of a satellite orbiting the Earth at a distance h from the surface of Earth is calculated as follows; the total energy of the satellite is the sum of its kinetic energy and the gravitational potential energy.

54. In which of this condition a satellite is free from the Earth’s gravity?

a) h approaches ∞

b) h approaches 0

c) h is maximum

d) None of the above

Explanation

The total energy of the satellite orbiting the Earth at a height of h is,

The negative sign in the total energy implies that the satellite is bound to the Earth and it cannot escape from the Earth. As h approaches ∞, the total energy tends to zero. Its physical meaning is that the satellite is completely free from the influence of Earth’s gravity and is not bound to Earth at large distances.

55. What is the value of h for the geo-stationary satellite?

a) 24 km

b) 86400 km

c) 36000 km

d) 100000 km

Explanation

Kepler’s third law is used to find the radius of the orbit.

Substituting for the time period (24 hrs = 86400 seconds), mass, and radius of the Earth, h turns out to be 36,000 km. Such satellites are called “geo-stationary satellites”, since they appear to be stationary when seen from Earth.

56. Which of the following statements are not true regarding the Polar satellites?

a) The polar satellites orbits earth from South Pole to North Pole.

b) The time period of a polar satellite is about 100 minutes.

c) The Polar satellites cover different small strips of earth area in each revolution.

d) Polar satellites cover only a small strip of area from pole to pole during one revolution.

Explanation

Earth orbits the Earth from north to south direction. This type of satellite that orbits Earth from North Pole to South Pole is called a polar satellite. The time period of a polar satellite is nearly 100 minutes and the satellite completes many revolutions in a day. A Polar satellite covers a small strip of area from pole to pole during one revolution. In the next revolution it covers a different strip of area since the Earth would have moved by a small angle. In this way polar satellites cover the entire surface area of the Earth.

57. Choose the correct statements.

i) All the objects anywhere in the solar system experience the gravitational force.

ii) The Earth gravitational force acts downwards towards the centre of the earth.

iii) There are number of forces acting on us when we stand on the floor in earth surface.

a) i only

b) ii only

c) iii only

d) All the above

Explanation

Objects on Earth experience the gravitational force of Earth. The gravitational force acting on an object of mass m is mg. This force always acts downwards towards the centre of the Earth. When we stand on the floor, there are two forces acting on us. One is the gravitational force, acting downwards and the other is the normal force exerted by the floor upwards on us to keep us at rest.

58. Assertion (A): The weight of an object is defined as the upward force with magnitude W is equal to the force.

Reasoning(R): Weight of an object is the upward force applied to hold it at rest or at constant velocity relative to earth.

a) Both A and R is True and R is the correct explanation of A.

b) Both A and R is True but R is not the correct explanation of A.

c) A is False but R is True.

d) Both A and R is False.

Explanation

The weight of an object W is defined as the downward force whose magnitude W is equal to that of upward force that must be applied to the object to hold it at rest or at constant velocity relative to the earth.

59. In which of this direction normal object weight is directed?

a) Upward force

b) Linear force

c) Gravitational force

d) Momentum

Explanation

The direction of weight is in the direction of gravitational force. So the magnitude of weight of an object is denoted as, W=N=mg

60. Choose the Incorrect statements.

i) A man standing in an elevator experiences two kinds of forces.

ii) Gravitational force on the man in an elevator is acting downwards to the ground.

iii) The Normal force exerted by the floor also acts downwards to the man in an elevator.

a) i only

b) ii only

c) iii only

d) None of the above

Explanation

61. Assertion (A): The Astronauts in the satellites do not experience any gravitational force due to the distance from the earth.

Reasoning(R): The Satellites orbit very close to Earth experience only gravitational force.

a) Both A and R is True and R is the correct explanation of A.

b) Both A and R is True but R is not the correct explanation of A.

c) A is True but R is False.

d) Both A and R is False.

Explanation

There is a wrong notion that the astronauts in satellites experience no gravitational force because they are far away from the Earth. Actually the Earth satellites that orbit very close to Earth experience only gravitational force. The astronauts inside the satellite also experience the same gravitational force. Because of this, they cannot exert any force on the floor of the satellite. Thus, the floor of the satellite also cannot exert any normal force on the astronaut. Therefore, the astronauts inside a satellite are in the state of weightlessness. Not only the astronauts, but all the objects in the satellite will be in the state of weightlessness which is similar to that of a free fall.

62. Towards which of this direction the planets move in the retrograde motion?

a) West

b) North

c) East

d) South

Explanation

When the motion of the planets are observed in the night sky by naked eyes over a period of a few months, it can be seen that the planets move eastwards and reverse their motion for a while and return to eastward motion again. This is called “retrograde motion” of planets.

63. From which month the Mars changes its direction from retrograde motion?

a) July

b) October

c) September

d) June

Explanation

Careful observation for a period of a year clearly shows that Mars initially moves eastwards (February to June), then reverses its path and moves backwards (July, August, September). It changes its direction of motion once again and continues its forward motion (October onwards).

64. Which of the following concept was introduced by Ptolemy to explain the retrograde motion of the planets?

a) Gravitational constant

b) Eclipse

c) Geo-stationary

d) Epicycle

Explanation

To explain this retrograde motion, Ptolemy introduced the concept of “epicycle” in his geocentric model. According to this theory, while the planet orbited the Earth, it also underwent another circular motion termed as “epicycle”.

65. Choose the incorrect statements.

i) The retrograde motion of the planets is a combination of epicycle and circular motion around the Earth.

ii) The Earth centric idea was introduced by Aristotle.

iii) Ptolemy’s model was very simple as every planet undergoes the retrograde motion.

a) i only

b) ii only

c) iii only

d) None of the above

Explanation

A combination of epicycle and circular motion around the Earth gave rise to retrograde motion of the planets with respect to Earth. Essentially Ptolemy retained the Earth centric idea of Aristotle and added the epicycle motion to it. Ptolemy’s model became more and more complex as every planet was found to undergo retrograde motion.

66. Which of these is the centre of the solar system according to the heliocentric model of Copernicus?

a) Earth

b) Sun

c) Mars

d) Jupiter

Explanation

In the 15^th century, the Polish astronomer Copernicus proposed the heliocentric model to explain this problem in a simpler manner. According to this model, the Sun is at the centre of the solar system and all planets orbited the Sun. The retrograde motion of planets with respect to Earth is because of the relative motion of the planet with respect to Earth.

67. Choose the correct statements.

i) Copernicus explained the retrograde motion of the Mars and Earth only.

ii) The Mars orbits around the Sun faster than the Earth.

iii) Mars appears to move backwards from July to October because of the relative motion of the Earth and Mars.

a) i only

b) ii only

c) iii only

d) All the above

Explanation

The Earth orbits around the Sun faster than Mars. Because of the relative motion between Mars and Earth, Mars appears to move backwards from July to October. In the same way the retrograde motion of all other planets was explained successfully by the Copernicus model.

68. What is the advantage of the heliocentric model?

a) Simple model

b) Accurate results

c) Explained all the forces involved

d) All the above

Explanation

It was because of its simplicity, the heliocentric model slowly replaced the geocentric model. Historically, if any natural phenomenon has one or more explanations, the simplest one is usually accepted.

69. Which of the following statement is not true?

a) Kepler relied on Tycho Brahe’s astronomical observations for his laws.

b) Kepler’s third law related the distances of a planet from the Sun to its revolution period.

c) The distance of the planet from the Sun is calculated in terms of the distance between Earth and the Sun.

d) The Astronomers used complex algorithms and calculations to calculate the distance of a planet from the Sun.

Explanation

When Kepler derived his three laws, he strongly relied on Tycho Brahe’s astronomical observation. In his third law, he formulated the relation between the distances of a planet from the Sun to the time period of revolution of the planet. Astronomers cleverly used geometry and trigonometry to calculate the distance of a planet from the Sun in terms of the distance between Earth and Sun.

70. What is the distance between the Earth and the Sun?

a) One Astronomical Unit

b) One Light year

c) One Parsec

d) One Solar Mass

Explanation

When Venus is at maximum elongation (i.e., 46 degree) with respect to Earth, Venus makes 90 degree to Sun. This allows us to find the distance between Venus and Sun. The distance between Earth and Sun is taken as one Astronomical unit (1 AU).

71. Which of the following planets have the highest value of the semi major axis of the orbit from the Sun?

a) Mars

b) Earth

c) Jupiter

d) Venus

72. Identify the Incorrect Match.

PLANETS TIME PERIOD

A. Saturn i) 4332.62

B. Mercury ii) 87.77

C. Venus iii) 224.70

D. Mars iv) 686.98

a) i only

b) ii only

c) iii only

d) iv only

Explanation

The distances of planets from the Sun are given in the table below.

73. Which of these values denotes the difference in sun ray shadow due to the curvature of the Earth?

a) 7.5 degree

b) 1/ 8 radian

c) 0.75 degree

d) 1/ 18 radian

Explanation

During noon time of summer solstice the Sun’s rays cast no shadow in the city Syne which was located 500 miles away from Alexandria. At the same day and same time he found that in Alexandria the Sun’s rays made 7.2 degree with local vertical. This difference of 7.2 degree was due to the curvature of the Earth. The angle 7.2 degree is equivalent to 1/8radian. So θ= 1/8 rad;

74. In which colour the moon will appear inside the umbra shadow?

a) Yellow

b) Blue

c) Red

d) Black

Explanation

When the Moon is inside the umbra shadow, it appears red in colour. As soon as the Moon exits from the umbra shadow, it appears in crescent shape.

75. Assertion (A): During the lunar eclipse the orbits of the Moon and Earth lie on the same plane on full moon day.

Reasoning(R): The Solar eclipse is observed during the new moon day.

a) Both A and R is True and R is the correct explanation of A.

b) Both A and R is True but R is not the correct explanation of A.

c) A is True but R is False.

d) Both A and R is False.

Explanation

If the orbits of the Moon and Earth lie on the same plane, during full Moon of every month, we can observe lunar eclipse. If this is so during new Moon we can observe solar eclipse.

76. Why Solar and Lunar eclipse occur only during certain periods of the year?

a) The earth revolution on its own axis.

b) The Orbit of Moon is tilted for 5° with respect to the Earth’s orbit.

c) The Gravitation field of the Earth and Moon are different.

d) Planets have different rotation period with respect to Earth.

Explanation

Moon’s orbit is tilted 5° with respect to Earth’s orbit. Due to this 5° tilt, only during certain periods of the year, the Sun, Earth and Moon align in straight line leading to either lunar eclipse or solar eclipse depending on the alignment.

77. Assertion (A): The Northern and the Southern part of the Earth experiences seasonal changes depending on the distance from the Sun.

Reasoning(R): The seasons in the Earth arise due to the rotation of the Earth around the Sun with 23.5° tilt.

a) Both A and R is True and R is the correct explanation of A.

b) Both A and R is True but R is not the correct explanation of A.

c) A is True but R is False.

d) Both A and R is False.

Explanation

The seasons in the Earth arise due to the rotation of Earth around the Sun with 23.5° tilt Due to this 23.5° tilt, when the northern part of Earth is farther to the Sun, the southern part is nearer to the Sun. So when it is summer in the northern hemisphere, the southern hemisphere experience winter.

78. Which of these can be explained by the spinning motion of Earth?

a) Sun light radiation

b) Solar eclipse

c) Position of Stars

d) Planets movement

Explanation

The Earth’s spinning motion can be proved by observing star’s position over a night. Due to Earth’s spinning motion, the stars in sky appear to move in circular motion about the pole star.

79. Name the pole star of the Earth.

a) Polaris

b) Alpha Pictoris

c) Delta Doradus

d) Draconis

Explanation

Pole star is a star located exactly above the Earth’s axis of rotation hence it appears to be stationary. The Star Polaris is our pole star.

80. Choose the Incorrect statements.

i) The Electromagnetic spectrum was discovered at the end of the 19^th century.

ii) Newton’s law of gravitation was able to explain the entire phenomenon related to gravity.

iii) Albert Einstein General relativity theory was the most successful theory in the 20^th century.

a) i only

b) ii only

c) iii only

d) None of the above

Explanation

After the discovery of the electromagnetic spectrum at the end of the 19th century, our understanding of the universe increased enormously. Because of this development in the late 19th century it was found that Newton’s law of gravitation could not explain certain phenomena and showed some discrepancies. Albert Einstein formulated his ‘General theory of relativity’ which was one of the most successful theories of 20th century in the field of gravitation.

81. For which of the following theories Subramanian Chandrasekhar was awarded Nobel Prize in the year 1983?

a) Black hole theory

b) Gravitational theory

c) Big Bang theory

d) Quantum field theory

Explanation

Subramanian Chandrasekhar formulated the theory of black holes and explained the life of stars. These studies brought him the Nobel Prize in the year 1983. Another very notable Indian astrophysicist Meghnad Saha discovered the ionization formula which was useful in classifying stars. This formula is now known as “Saha ionization formula”.

82. Choose the correct statements.

i) Amal Kumar Raychaudhuri solved an equation, Raychaudhuri equation in the field of gravitation.

ii) The Astrophysicist Jayant V Narlikar wrote books on astronomy and astrophysics.

a) i only

b) ii only

c) Both i and ii

d) Neither i nor ii

Explanation

In the field of gravitation Amal Kumar Raychaudhuri solved an equation now known as “Raychaudhuri equation” which was a very important contribution. Another notable Indian Astrophysicist Jayant V Narlikar made pioneering contribution in the field of astrophysics and has written interesting books on astronomy and astrophysics.

83. Who founded the Inter University Centre for Astronomy and Astrophysics, India?

a) Homi Jahangir Bhabha

b) J.V. Narlikar

c) Jagadish Chandra Bose

d) C.V. Raman

Explanation

IUCAA (Inter University Centre for Astronomy and Astrophysics) is one of the important Indian research institutes where active research in astrophysics and gravitation are conducted. The institute was founded by Prof. J.V. Narlikar. Students are encouraged to read more about the recent developments in these fields.

84. In which year Albert Einstein theoretically predicted the Gravitational waves?

a) 1915

b) 1923

c) 1901

d) 1821

Explanation

The Nobel Prize in Physics was given for the detection of ‘Gravitational waves’ which was theoretically predicted by Albert Einstein in the year 1915.

85. Which of the following statements is true?

a) Tycho Brahe analyzed and deducted of the laws of the planetary motion.

b) Claudius Ptolemy, an American astronomer developed the heliocentric model.

c) Ptolemy’s model successfully explained the motion of Mars and Jupiter.

d) The Sun is at the center of the solar system in the heliocentric model.

Explanation

Ptolemy’s model successfully explained the motion of the Sun and the Moon up to a certain level, the motion of Mars and Jupiter could not be explained effectively. In the second century, Claudius Ptolemy, a famous Greco-Roman astronomer developed a theory to explain the motion of celestial objects like the Sun, the Moon, Mars, and Jupiter etc. This theory was called the geocentric model. Nicholas Copernicus (1473-1543) proposed a new model called the ‘Heliocentric model’ in which the Sun was considered to be at the center of the solar system. Tycho Brahe (1546-1601) spent his entire lifetime in recording the observations of the stellar and planetary positions with his naked eye.

86. State the mathematical form of the newton’s law of gravitation?

a) GM² / r³

b) G r²/ M₁M₂

c) – (GM₁M₂/r²) r^{^}

d) GM₁M₂r²

Explanation

In mathematical form, the Newton’s law of gravitation can be written as:

87. Which of the following is led by the constancy of angular momentum of all planets?

a) Newton’s third law

b) Heliocentric model

c) Kepler’s Second law

d) Gravitational constant

Explanation

The angular momentum of the Earth about the Sun is constant throughout the motion. It is true for all the planets. In fact, this constancy of angular momentum leads to the Kepler’s second law.

88. State the distance between the moon and earth based on Hipparchrus measurement?

a) 60 times the radius of Earth.

b) Double the distance between Earth and the Sun.

c) Time duration of sunlight to reach earth.

d) Distance between Sun and Moon.

Explanation

From the Hipparchrus measurement, the distance to the Moon is 60 times that of Earth radius. Rm = 60R.

89. In how many days moon orbits the earth?

a) Twice in 15 days.

b) Once in 20.7 days.

c) Once in 27.3days.

d) Twice in 27.3days.

Explanation

Moon orbits the Earth once in 27.3 days and by using the centripetal acceleration formula.

90. Which of the following is explained by the concept of gravitational field?

a) Field intensity due to a mass.

b) Non-contact interaction between two mass.

c) Earth orbiting around the Sun.

d) Force between Moon and the Earth.

Explanation

The non-contact interaction between two masses can now be explained using the concept of “Gravitational field”.

91. Which of these methods is used to find the gravitational field at any point for continuous distribution of total mass?

a) Integration

b) Point distribution

c) Differentiation

d) None of the above

Explanation

Instead of discrete masses, if continuous distribution of total masses is considered then the gravitational field at a point is calculated using the method of integration.

92. What is the value of the gravitational potential energy of a two mass system separated by a distance?

a) Either negative or positive

b) Always negative

c) Always maximum

d) Depends on the value of mass

Explanation

Gravitational potential energy of a system of two masses m1 and m2 separated by a distance r as the amount of work done to take the mass m2 from a distance r to infinity assuming m1 to be fixed in its position. The gravitational potential energy is always negative because when two masses come together slowly from infinity, work is done by the system.

93. State the value of gravitational potential energy on the surface of the earth?

a) mgh

b) 0

c) ∞

d) mv²

Explanation

The gravitational potential energy stored in the particle of mass m at a height h from the surface of the Earth is U=mgh. On the surface of the Earth, U = 0, since h is zero.

94. At which points the acceleration due to gravity decreases in earth?

a) In upward direction from earth surface

b) On the surface of earth

c) Towards downward from the surface of earth

d) Both a and c

Explanation

Acceleration due to gravity is maximum on the surface of the Earth but decreases when we go either upward or downward.

95. Choose the incorrect statements.

i) Satellites revolve around the Earth as like the planets revolve around the Sun.

ii) Kepler’s laws are not applicable to the man-made satellites.

a) i only

b) ii only

c) Both I and ii

d) Neither i nor ii

Explanation

Satellites revolve around the Earth just like the planets revolve around the Sun. Kepler’s laws are applicable to man-made satellites also.

11th Science Lesson 6 Questions in English

6] Heat And Thermodynamics

1. Which of the following statement is incorrect?

Temperature and heat play very important role in everyday life
Life on Earth is possible because the Sun maintains its temperature
1 alone
2 alone
1, 2
None

Explanation

Temperature and heat play very important role in everyday life. All species can function properly only if its body is maintained at a particular temperature. In fact, life on Earth is possible because the Sun maintains its temperature.

2. ______ is a branch of physics which explains the phenomena of temperature, heat

Kinematics
Thermodynamics
Acoustics
Sonography

Explanation

Understanding the meaning of temperature and heat are very crucial to understand the nature. Thermodynamics is a branch of physics which explains the phenomena of temperature, heat etc.

3. In thermodynamics, heat and temperature are two_____ parameters

Same and closely related
Different and closely related
Different and unrelated
Same and unrelated

Explanation

The concepts presented in this chapter will help us to understand the terms ‘hot’ and ‘cold’ and also differentiate heat from temperature. In thermodynamics, heat and temperature are two different but closely related parameters.

4. Which of the following statement is correct?

Energy flows spontaneously from lower temperature object to higher temperature object
This flow of energy is called heat
Due to flow of heat sometimes the temperature of the body will increase or sometimes it may not increase.
1, 2
1, 3
2, 3
All the above

Explanation

When an object at higher temperature is placed in contact with another object at lower temperature, there will be a spontaneous flow of energy from the object at higher temperature to the one at lower temperature. This energy is called heat. This process of energy transfer from higher temperature object to lower temperature object is called heating. Due to flow of heat sometimes the temperature of the body will increase or sometimes it may not increase.

5. Which of the following statement is correct?

People often talk ‘this water has more heat or less heat’.
There is a misconception that heat is a quantity of energy
When we use the word ‘heat’, it is the energy in transit but not energy stored in the body.
1, 2
1, 3
2, 3
All the above

Explanation

There is a misconception that heat is a quantity of energy. People often talk ‘this water has more heat or less heat’. These words are meaningless. Heat is not a quantity. Heat is an energy in transit which flows from higher temperature object to lower temperature object. Once the heating process is stopped, we cannot use the word heat. When we use the word ‘heat’, it is the energy in transit but not energy stored in the body.

6. Which of the following statement is correct?

When you rub your hands against each other the temperature of the hands increases.
The temperature of the hands increases due to this work.
1 alone
2 alone
1, 2
None

Explanation

When you rub your hands against each other the temperature of the hands increases. You have done some work on your hands by rubbing. The temperature of the hands increases due to this work. Now if you place your hands on the chin, the temperature of the chin increases. This is because the hands are at higher temperature than the chin.

7. Which of the following statement is incorrect?

By doing work on the system, the temperature in the system will increase and sometimes may not
Work is a quantity
1 alone
2 alone
1, 2
None

Explanation

By doing work on the system, the temperature in the system will increase and sometimes may not. Like heat, work is also not a quantity and through the work energy is transferred to the system. So, we cannot use the word ‘the object contains more work’ or ‘less work’.

8. For the transfer of energy from one body to another body through the process of work, they should

be at______ temperatures

Same
Different
Slightly equal
None

Explanation

Either the system can transfer energy to the surrounding by doing work on surrounding or the surrounding may transfer energy to the system by doing work on the system. For the transfer of energy from one body to another body through the process of work, they need not be at different temperatures.

9. Which of the following statement is correct?

Temperature is the degree of hotness or coolness of a body
The temperature will determine the direction of heat flow when two bodies are in thermal contact
1 alone
2 alone
1, 2
None

Explanation

Temperature is the degree of hotness or coolness of a body. Hotter the body higher is its temperature. The temperature will determine the direction of heat flow when two bodies are in thermal contact.

10. The SI unit of temperature is_____

K
°F
˚C
All the above

Explanation

The SI unit of temperature is kelvin (K). In our day to day applications, Celsius (˚C) and Fahrenheit (°F) scales are used. Temperature is measured with a thermometer.

11. Which of the following temperature conversion is correct?

Celsius to Kelvin K=°C + 273.15
Celsius to Fahrenheit °C = (°F − 32) ÷ 1.8
1 alone
2 alone
1, 2
None

Explanation

12. According to Boyle’s law_______

Pressure of the gas is inversely proportional to the volume
Volume of the gas is directly proportional to absolute temperature
Volume of gas is inversely proportional to absolute temperature
Pressure of the gas is directly proportional to the volume

Explanation

When the gas is kept at constant temperature, the pressure of the gas is inversely proportional to the volume. P α 1/ V. It was discovered by Robert Boyle (1627-1691) and is known as Boyle’s law.

13. According to Charles’ law_____

Pressure of the gas is inversely proportional to the volume
Volume of the gas is directly proportional to absolute temperature
Volume of gas is inversely proportional to absolute temperature
Pressure of the gas is directly proportional to the volume

Explanation

When the gas is kept at constant pressure, the volume of the gas is directly proportional to absolute temperature. V α T. It was discovered by Jacques Charles (1743-1823) and is known as Charles’ law.

14. Which of the following is ideal gas law?

PV = N k T
PV = N T
PV/ T = N k
PV = N k/ T

Explanation

By combining Boyle’s law, Charles’ law equations we have ideal gas law. So the ideal gas law can be stated as follows:

PV = N k T

15. Boltzmann constant is equal to_________

1.381 × 10⁻²³ JK⁻¹
1.381 × 10⁻²³ JK
1.608 × 10¹⁸JK
1.608 × 10^-18JK^-1

Explanation

Ideal gas equation:

PV = N k T

Here k is the Boltzmann constant (1.381×10⁻²³ JK⁻¹) and it is found to be a universal constant.

16. Which of the following statement is correct?

Atom is the practical unit to express the amount of gas
One mole of any substance is the amount of that substance which contains Avogadro number (N_A) of particles
1 alone
2 alone
1, 2
None

Explanation

Mole is the practical unit to express the amount of gas. One mole of any substance is the amount of that substance which contains Avogadro number (N_A) of particles (such as atoms or molecules).

17. The Avogadro number is defined as the number of carbon atoms contained in exactly ___g of ¹²C

Explanation

The Avogadro’s number NA is defined as the number of carbon atoms contained in exactly 12 g of ¹²C. One mole of any substance is the amount of that substance which contains Avogadro number (NA) of particles (such as atoms or molecules).

18. Avogadro number is equal to_____

6.023 ×10²³ mol
6.023 ×10²³mol^–1
5.023 ×10²³mol^–1
4.023 ×10²³mol^–1

Explanation

Suppose if a gas contains μ mole of particles then the total number of particles can be written as

N = μ N_A

where N_A is Avogadro number (6.023 ×10²³mol^–1)

19. Universal gas constant is equal to_____

6.023 ×10²³ mol
8.314 J /mol. K
7.314 J /mol. K
6.314 J /mol. K

Explanation

PV = μ N A k T. Here N A k=R called universal gas constant and its value is 8.314 J /mol. K. So, the ideal gas law can be written for μ mole of gas as

PV = μ R T

20. Which equation relates the pressure, volume and temperature of thermodynamic system at

equilibrium?

Boyle’s equation
Charles’ equation
Ideal gas equation
None

Explanation

PV = μ R T

This is called the equation of state for an ideal gas. It relates the pressure, volume and temperature of thermodynamic system at equilibrium.

21. A student comes to school by a bicycle whose tire is filled with air at a pressure 240 kPa at 27°C.

She travels 8 km to reach the school and the temperature of the bicycle tire increases to 39°C.

What is the change in pressure in the tire when the student reaches school?

270 Pa
249.6 Pa
230.6 Pa
210.1 Pa

Explanation

22. When a person breathes, his lungs can hold up to 5.5 Litre of air at body temperature 37°C and

atmospheric pressure (1 atm =101 kPa). This Air contains 21% oxygen. Calculate the number of

oxygen molecules in the lungs.

2.7× 10²²
3.7× 10²¹
1.7× 10²²
2.7× 10²¹

Explanation

23. Calculate the volume of one mole of any gas at STP and at room temperature (300K) with the

same pressure 1 atm.

22.4 × 10^–3 m³
22.4 × 10^–3 m²
12.4 × 10^–3 m³
22.4 × 10^–3 m^-3

Explanation

24. 1 Litre (L) =______

10^–3m³
10³m³
10^–3m^-3
10³m^-3

Explanation

25. _____% of Oxygen present in air

Explanation

Air is the mixture of about 20% oxygen, 79% nitrogen and remaining one percent are argon, hydrogen, helium, and xenon. The molar mass of air is 29 g mol^–1.

26. _____ is defined as amount of heat energy required to raise the temperature of the given body

from T to T + ∆T

Heat capacity
Radiation
Specific heat capacity
Sublimation

Explanation

We can define ‘heat capacity’ as the amount of heat energy required to raise the temperature of the given body from T to T + ∆T. Specific heat capacity of a substance is defined as the amount of heat energy required to raise the temperature of 1kg of a substance by 1 Kelvin or 1°C

27. The SI unit for specific heat capacity is______

J kg ^–1 K^–1
J kg ^–1 K
kg K^–1
J kg K–1

Explanation

The SI unit for specific heat capacity is J kg ^–1 K^–1. Heat capacity and specific heat capacity are always positive quantities.

28. Match the specific heat capacity with respective material

Air 1. 130
Lead 2. 4186
Human body 3. 1005
Water 4. 3470
2, 1, 3, 4
3, 1, 4, 2
3, 4, 1, 2
3, 2, 1, 4

Explanation

29. Which of the following statement is correct?

The term heat capacity or specific heat capacity does not mean that object contains a certain amount of heat
Heat is energy transfer from the object at higher temperature to the object at lower temperature
1 alone
2 alone
1, 2
None

Explanation

The term heat capacity or specific heat capacity does not mean that object contains a certain amount of heat. Heat is energy transfer from the object at higher temperature to the object at lower temperature. The correct usage is ‘internal energy capacity’. But for historical reason the term ‘heat capacity’ or ‘specific heat capacity’ are retained.

30. The SI unit for molar specific heat capacity is_____

J mol
J mol^–1 K^–1
J mol^–1
J mol K^–1

Explanation

The SI unit for molar specific heat capacity is J mol^–1 K^–1. It is also a positive quantity. When we study properties of gases, it is more practical to use molar specific heat capacity.

31. Thermal expansion is the tendency of matter to change in___ due to change in temperature

Volume
Shape
Area
1, 2
2, 3
1, 3
All the above

Explanation

Thermal expansion is the tendency of matter to change in shape, area, and volume due to a change in temperature.

32. Which of the following will expand when heated?

Solid
Liquid
Gas
1, 2
1, 3
2, 3
All the above

Explanation

All three states of matter (solid, liquid and gas) expand when heated. When a solid is heated, its atoms vibrate with higher amplitude about their fixed points.

33. Which of the following expands more?

Solid
Liquid
Gas
All the above

Explanation

Liquids, have less intermolecular forces than solids and hence they expand more than solids. This is the principle behind the mercury thermometers. In the case of gas molecules, the intermolecular forces are almost negligible and hence they expand much more than solids.

34. Which of the following statement is correct?

The increase in dimension of a body due to the increase in its temperature is called thermal expansion
The expansion in length is called area expansion
1 alone
2 alone
1, 2
None

Explanation

The increase in dimension of a body due to the increase in its temperature is called thermal expansion. The expansion in length is called linear expansion. Similarly, the expansion in area is termed as area expansion.

35. Which of the following statement is incorrect?

When the lid of a glass bottle is tight, keep the lid near the hot water which makes it easier to open.
When the hot boiled egg is dropped in cold water, the egg shell can be removed easily.
1 alone
2 alone
1, 2
None

Explanation

When the lid of a glass bottle is tight, keep the lid near the hot water which makes it easier to open. It is because the lid has higher thermal expansion than glass. When the hot boiled egg is dropped in cold water, the egg shell can be removed easily. It is because of the different thermal expansions of the shell and egg.

36. Eiffel tower is made up of iron and its height is roughly 300 m. During winter season (January) in France the temperature is 2°C and in hot summer its average temperature 25°C. Calculate the

change in height of Eiffel tower between summer and winter.

89 mm
69 mm
39 mm
29 mm

Explanation

The linear thermal expansion coefficient for iron α = 10 ×10−6 per °C

37. Which of the following statement is correct?

Liquids expand on heating and contract on cooling at moderate temperatures.
water exhibits an anomalous behaviour
1 alone
2 alone
1, 2
None

Explanation

Liquids expand on heating and contract on cooling at moderate temperatures. But water exhibits an anomalous behaviour.

38. Water contracts on heating between___ ^oC and __ ^o C

4, 10
0, 4
2, 5
3, 12

Explanation

Water contracts on heating between 0˚C and 4˚C. The volume of the given amount of water decreases as it is cooled from room temperature, until it reaches 4˚C.

39. Water has maximum density at_____ ^o C

Explanation

Below 4˚C the volume increases and so the density decreases. This means that the water has a maximum density at 4˚C. This behaviour of water is called anomalous expansion of water.

40. Match the following

Melting 1. gas to liquid
Sublimation 2. solid to liquid
Condensation 3. solid to gas
Freezing 4. liquid to solid
2, 1, 3, 4
4, 1, 2, 3
2, 3, 1, 4
1, 2, 3, 4

Explanation

All matter exists normally in three states as solids, liquids or gases. Matter can be changed from one state to another either by heating or cooling.

1. Melting (solid to liquid) 2. Evaporation (liquid to gas) 3. Sublimation (solid to gas) 4. Freezing / Solidification (liquid to solid) 5. Condensation (gas to liquid)

41. Boiling point of water____ ⁰ C

99
100
103
90

Explanation

While boiling a pot of water, the temperature of the water increases until it reaches 100 ˚C which is the boiling point of water, and then the temperature remains constant until all the water changes from liquid to gas.

42. ____of a substance is defined as the amount of heat energy required to change the state of a unit

mass of the material

Specific heat capacity
Latent heat capacity
Thermal resistance
Specific heat

Explanation

Latent heat capacity of a substance is defined as the amount of heat energy required to change the state of a unit mass of the material.

43. The SI unit for Latent heat capacity is_____

J mol
J mol^-1
J kg^-1
J K^-1

Explanation

The temperature of water does not increase above its boiling point. This is the concept of latent heat capacity. The SI unit for Latent heat capacity is J kg^–1.

44. Match the following

Latent heat for a solid – liquid state change 1. latent heat of sublimation
Latent heat for a liquid – gas state change 2. latent heat of fusion
Latent heat for a solid – gas state change 3. latent heat of vaporization
2, 1, 3
2, 3, 1
1, 3, 2
3, 1, 2

Explanation

• The latent heat for a solid – liquid state change is called the latent heat of fusion (Lf) • The latent heat for a liquid – gas state change is called the latent heat of vaporization (Lv) • The latent heat for a solid – gas state change is called the latent heat of sublimation (Ls).

45. The triple point of water is at_____ K

273.1
289.2
223.1
289.3

Explanation

Triple point of a substance is the temperature and pressure at which the three phases (gas, liquid and solid) of that substance coexist in thermodynamic equilibrium. The triple point of water is at 273.1 K and a partial vapour pressure of 611.657 Pascal.

46. _____ means the measurement of the amount of heat released or absorbed by thermodynamic

system during the heating process.

Calorimetry
Manometry
Nemometry
Calsometry

Explanation

Calorimetry means the measurement of the amount of heat released or absorbed by thermodynamic system during the heating process. When a body at higher temperature is brought in contact with another body at lower temperature, the heat lost by the hot body is equal to the heat gained by the cold body.

47. Heat gained or lost is measured with a______

Thermometer
Pulse-oximeter
Calorimeter
Nanometre

Explanation

Heat gained or lost is measured with a calorimeter. Usually, the calorimeter is an insulated container of water.

48. If 5 L of water at 50°C is mixed with 4L of water at 30°C, what will be the final temperature of

water? Take the specific heat capacity of water as 4184 J kg^-1 K^-1.

100 ^o C
40 ^oC
30 ^o C
70 ^oC

Explanation

49. Final equilibrium temperature of mixing of gas or liquid depends on_____

Mass of the substance
Specific heat capacity
Temperature
1, 2
1, 3
2, 3
All the above

Explanation

It is important to note that the final equilibrium temperature of mixing of gas or liquid depends on mass of the substances, their specific heat capacities and their temperatures. Only if we mix the same substances at equal amount, the final temperature will be an average of the individual temperatures.

50. How many modes of heat transfer are there?

Explanation

As we have seen already heat is a energy in transit which is transferred from one body to another body due to temperature difference. There are three modes of heat transfer: Conduction, Convection and Radiation.

51. ____ is the process of direct transfer of heat through matter due to temperature difference

Radiation
Conduction
Convection
All the above

Explanation

Conduction is the process of direct transfer of heat through matter due to temperature difference. When two objects are in direct contact with one another, heat will be transferred from the hotter object to the colder one. The objects which allow heat to travel easily through them are called conductors.

52. Which of the following statement is correct?

Thermal conductivity is the ability to conduct heat.
The quantity of heat transferred through a unit length of a material in a direction normal to unit surface area due to a unit temperature difference under steady state conditions
1 alone
2 alone
1, 2
None

Explanation

Thermal conductivity is the ability to conduct heat. The quantity of heat transferred through a unit length of a material in a direction normal to unit surface area due to a unit temperature difference under steady state conditions is known as thermal conductivity of a material.

53. The SI unit of thermal conductivity is______

J s^-1 m^-1
J s-1 m K^-1
J s m K^-1
J s^-1 m^-1 K^-1

Explanation

In steady state, the rate of flow of heat Q is proportional to the temperature difference ΔT and the area of cross section A and is inversely proportional to the length L. The SI unit of thermal conductivity is J s^-1 m^-1 K^-1 or W m^-1 K^-1.

54. Match the thermal conductivity of the material

Silver 1. 2
Copper 2. 2300
Diamond 3. 380
Ice 4. 420
3, 1, 2, 4
4, 3, 2, 1
2, 1, 4, 3
4, 2, 3, 1

Explanation

55. Match the following

Water 1. 0.042
Air 2. 0.56
Helium 3. 0.023
Cork 4. 0.152
2, 1, 3, 4
2, 3, 4, 1
2, 1, 4, 3
3, 2, 1, 4

Explanation

56. Which of the following have high thermal conductivity?

Silver
Nickel
Aluminium
Both a and c

Explanation

Thermal conductivity depends on the nature of the material. For example, silver and aluminium have high thermal conductivities. So, they are used to make cooking vessels.

57. Convection is the process in which heat transfer is by actual movement of molecules in___

Solid
Liquid
Gas
Fluid

Explanation

Convection is the process in which heat transfer is by actual movement of molecules in fluids such as liquids and gases. In convection, molecules move freely from one place to another. It happens naturally or forcefully.

58. Which of the following statement is correct?

During the day, sun rays warm up the land more quickly than sea water
It is because water has less specific heat capacity than land
1 alone
2 alone
1, 2
None

Explanation

During the day, sun rays warm up the land more quickly than sea water. It is because land has less specific heat capacity than water. As a result, the air above the land becomes less dense and rises.

59. The cooler air above the sea flows to land and it is called____

Land breeze
Sea breeze
Both a and b
None

Explanation

During the day, sun rays warm up the land more quickly than sea water. It is because land has less specific heat capacity than water. As a result the air above the land becomes less dense and rises. At the same time the cooler air above the sea flows to land and it is called ‘sea breeze’.

60. Which of the following statement is correct?

During the night time the land gets cooled faster than sea due to specific heat.
The air molecules above sea are warmer than air molecules above the land
1 alone
2 alone
1, 2
None

Explanation

During the night time the land gets cooled faster than sea due to the same reason (specific heat). The air molecules above sea are warmer than air molecules above the land. So, air molecules above the sea are replaced by cooler air molecules from the land. It is called ‘land breeze’

61. Water at the bottom of the pot receives_____

Less heat
More heat
Medium heat
None

Explanation

Boiling water in a cooking pot is an example of convection. Water at the bottom of the pot receives more heat.

62. Due to heating, the water_____ and the density of water increases at the bottom

Expands, increases
Contracts, increases
Expands, decreases
Contracts, decreases

Explanation

Boiling water in a cooking pot is an example of convection. Water at the bottom of the pot receives more heat. Due to heating, the water expands and the density of water decreases at the bottom. Due to this decrease in density, molecules rise to the top.

63. Which of the following statement is correct?

When we keep our hands near the hot stove we feel the heat even though our hands are not touching the hot stove.
Heat transferred from the hot stove to our hands is in the form of radiation
1 alone
2 alone
1, 2
None

Explanation

When we keep our hands near the hot stove we feel the heat even though our hands are not touching the hot stove. Here heat transferred from the hot stove to our hands is in the form of radiation. We receive energy from the sun in the form of radiations.

64. Radiation is a form of energy transfer from one body to another by_______

Radio waves
Electromagnetic waves
Ultrasonic waves
Infrasonic waves

Explanation

The conduction or convection requires medium to transfer the heat. Radiation is a form of energy transfer from one body to another by electromagnetic waves.

65. Which of the following statement is correct?

The parameter temperature is generally thought to be associated with matter
The visible radiation coming from the Sun is at the temperature of 570 K
Earth re emits the radiation in the infrared range into space which is at a temperature of around 300K.
1, 2
1, 3
2, 3
All the above

Explanation

The parameter temperature is generally thought to be associated with matter (solid, liquid and gas). But radiation is also considered as a thermodynamic system which has well defined temperature and pressure. The visible radiation coming from the Sun is at the temperature of 5700 K and the Earth re emits the radiation in the infrared range into space which is at a temperature of around 300K.

66. Which of the following statement is correct?

Newton’s law of cooling states that the rate of loss of heat of a body is directly proportional to the difference in the temperature between that body and its surroundings
Newton’s law of cooling states that the rate of loss of heat of a body is indirectly proportional to the difference in the temperature between that body and its surroundings
1 alone
2 alone
1, 2
None

Explanation

Newton’s law of cooling states that the rate of loss of heat of a body is directly proportional to the difference in the temperature between that body and its surroundings

67. Which of the following statement is correct?

Every object emits heat radiations at all finite temperatures (except 0 K) as well as it absorbs radiations from the surroundings
If you touch someone, they might feel your skin as either hot or cold is an example
1 alone
2 alone
1, 2
None

Explanation

Every object emits heat radiations at all finite temperatures (except 0 K) as well as it absorbs radiations from the surroundings. For example, if you touch someone, they might feel your skin as either hot or cold.

68. A body at high temperature_____ to the surroundings

Radiates more heat
Absorbs more heat
Radiates less heat
Absorbs less heat

Explanation

A body at high temperature radiates more heat to the surroundings than it receives from it. Similarly, a body at a lower temperature receives more heat from the surroundings than it loses to it.

69. Which of the following statement is correct?

Prevost applied the idea of ‘thermal equilibrium’ to radiation
He suggested that all bodies radiate energy but hot bodies radiate more heat than the cooler bodies.
Only at absolute zero temperature a body will stop emitting
1, 2
1, 3
2, 3
All the above

Explanation

Prevost applied the idea of ‘thermal equilibrium’ to radiation. He suggested that all bodies radiate energy but hot bodies radiate more heat than the cooler bodies. At one point of time the rate of exchange of heat from both the bodies will become the same. Now the bodies are said to be in ‘thermal equilibrium’. Only at absolute zero temperature a body will stop emitting. Therefore, Prevost theory states that all bodies emit thermal radiation at all temperatures above absolute zero irrespective of the nature of the surroundings.

70. Which equation about Stefan Boltzmann law is correct?

E ∝ T⁴
E ∝ T³
E ∝ T⁶
E ∝ T²

Explanation

Stefan Boltzmann law states that, the total amount of heat radiated per second per unit area of a black body is directly proportional to the fourth power of its absolute temperature.

71. E = e σ T4, e in the equation is_____

Emissivity
Energy
Electron
Emergence

Explanation

72. The wavelengths of radiations depend on the object’s______

Temperature
Absolute temperature
Mass
Gravitation

Explanation

In the universe every object emits radiation. The wavelengths of these radiations depend on the object’s absolute temperature. These radiations have different wavelengths and all the emitted wavelengths will not have equal intensity.

73. Which of the following statement is correct?

Wien’s law states that, the wavelength of maximum intensity of emission of a black body radiation is directly proportional to the absolute temperature of the black body
Wien’s law states that, the wavelength of maximum intensity of emission of a black body radiation is inversely proportional to the absolute temperature of the black body
1 alone
2 alone
1, 2
None

Explanation

Wien’s law states that, the wavelength of maximum intensity of emission of a black body radiation is inversely proportional to the absolute temperature of the black body

74. Wien constant value is____

2.898× 10^-7 m K
2.898× 10^-2 m K
2.898× 10^-5 m K
2.898× 10^-3 m K

Explanation

Where, b is known as Wien’s constant. Its value is 2.898× 10^-3 m K It implies that if temperature of the body increases, maximal intensity wavelength (λ m) shifts towards lower wavelength (higher frequency) of electromagnetic spectrum.

75. Which of the following statement is correct?

The Sun is approximately taken as a black body.
It is the wavelength at which maximum intensity is 508nm
Since the Sun’s temperature is around 5700K, the spectrum of radiations emitted by Sun lie

between 400 nm to 700 nm which is the visible part of the spectrum

1, 2
1, 3
2, 3
All the above

Explanation

The Sun is approximately taken as a black body. Since any object above 0 K will emit radiation, Sun also emits radiation. Its surface temperature is about 5700 K. It is the wavelength at which maximum intensity is 508nm. Since the Sun’s temperature is around 5700K, the spectrum of radiations emitted by Sun lie between 400 nm to 700 nm which is the visible part of the spectrum.

76. Which of the following statement is correct?

The humans evolved under the Sun by receiving its radiations.
Suppose if humans had evolved in a planet near the star Sirius (9940K), then they would have had the ability to see the Ultraviolet rays
1 alone
2 alone
1, 2
None

Explanation

The humans evolved under the Sun by receiving its radiations. The human eye is sensitive only in the visible not in infrared or X-ray ranges in the spectrum. Suppose if humans had evolved in a planet near the star Sirius (9940K), then they would have had the ability to see the Ultraviolet rays.

77. _____ branch of physics deals with laws governing the process of conversion of work into heat

and conversion of heat into work

Kinematics
Thermodynamics
Sonography
Kinetics

Explanation

Thermodynamics is a branch of physics which describes the laws governing the process of conversion of work into heat and conversion of heat into work.

78. Who among the following formulated laws of thermodynamics?

Boyle
Charles
Kelvin
1, 2
1, 3
2, 3
All the above

Explanation

The laws of thermodynamics are formulated over three centuries of experimental works of Boyle, Charles, Bernoulli, Joule, Clausius, Kelvin, Carnot and Helmholtz. In our day to day life, the functioning of everything around us and even our body is governed by the laws of thermodynamics.

79. Which of the following parameters can be used to specify thermodynamics?

Volume
Temperature
Pressure
1, 2
1, 3
2, 3
All the above

Explanation

A thermodynamic system is a finite part of the universe. It is a collection of large number of particles (atoms and molecules) specified by certain parameters called pressure (P), Volume (V) and Temperature (T). The remaining part of the universe is called surrounding. Both are separated by a boundary.

80. Which of the following are thermodynamic system?

Bucket of water
Sea of water
Human body
1, 2
1, 3
2, 3
All the above

Explanation

81. Which of the following statement is correct?

Open system can exchange both matter and energy with the environment
Isolated system can exchange neither energy nor matter with the environment
1 alone
2 alone
1, 2
None

Explanation

Open system can exchange both matter and energy with the environment. Closed system exchange energy but not matter with the environment. Isolated system can exchange neither energy nor matter with the environment.

82. When a hot cup of coffee is kept in the room, heat flows from______

Coffee to air
Air to coffee
Wise-versa
None

Explanation

When a hot cup of coffee is kept in the room, heat flows from coffee to the surrounding air. After sometime the coffee reaches the same temperature as the surrounding air and there will be no heat flow from coffee to air or air to coffee. It implies that the coffee and surrounding air are in thermal equilibrium with each other.

83. Two systems are said to be in thermal equilibrium with each other if they are at____ temperature

Different
Same
Slightly different
None

Explanation

Two systems are said to be in thermal equilibrium with each other if they are at the same temperature, which will not change with time.

84. Which of the following statement is correct?

A system is said to be in mechanical equilibrium if no unbalanced force acts on the thermo dynamic system or on the surrounding by thermodynamic system
When some mass is placed on the piston where filled with gas, it will move downward due to downward gravitational force and after certain humps and jumps the piston will come to rest at a new position
1 alone
2 alone
1, 2
None

Explanation

Consider a gas container with piston as shown in Figure 8.17. When some mass is placed on the piston, it will move downward due to downward gravitational force and after certain humps and jumps the piston will come to rest at a new position. When the downward gravitational force given by the piston is balanced by the upward force exerted by the gas, the system is said to be in mechanical equilibrium. A system is said to be in mechanical equilibrium if no unbalanced force acts on the thermo dynamic system or on the surrounding by thermodynamic system.

85. If two systems are set to be in thermodynamic equilibrium, then the systems are at____

Equilibrium

Thermal
Mechanical
Chemical
All the above

Explanation

If two systems are set to be in thermodynamic equilibrium, then the systems are at thermal, mechanical and chemical equilibrium with each other. In a state of thermo-dynamic equilibrium the macroscopic variables such as pressure, volume and temperature will have fixed values and do not change with time.

86. In mechanics, which of the following are used to explain the state of any moving object?

Velocity
Mass
Momentum
Acceleration
1, 2, 3
1, 3, 4
2, 3, 4
1, 2, 4

Explanation

In mechanics velocity, momentum and acceleration are used to explain the state of any moving object. If there is no net chemical reaction between two thermodynamic systems in contact with each other then it is said to be in chemical equilibrium.

87. Which of the following are thermodynamic variables?

Pressure
Volume
Internal energy
All the above

Explanation

In thermodynamics, the state of a thermodynamic system is represented by a set of variables called thermodynamic variables. Examples: Pressure, temperature, volume and internal energy, etc.

88. Which of the following are process variables in thermodynamics?

Work
Pressure
Heat
1, 2
1, 3
2, 3
All the above

Explanation

The values of these variables completely describe the equilibrium state of a thermodynamic system. Heat and work are not state variables rather they are process variables.

89. Which of the following statement is correct?

Extensive variable depends on the size or mass of the system
Temperature and pressure are examples of extensive variable
1 alone
2 alone
1, 2
None

Explanation

Extensive variable depends on the size or mass of the system. Example: Volume, total mass, entropy, internal energy, heat capacity etc.

90. Which of the following statement is correct?

Intensive variables depend on the size or mass of the system.
Example are Temperature, pressure, specific heat capacity, density etc.
1 alone
2 alone
1, 2
None

Explanation

Intensive variables do not depend on the size or mass of the system. Example: Temperature, pressure, specific heat capacity, density etc.

91. Which of the following statement is correct?

The equation which connects the state variables in a specific manner is called equation of state
A thermodynamic equilibrium is completely specified by pressure, volume, temperature state variables by the equation of state
1 alone
2 alone
1, 2
None

Explanation

The equation which connects the state variables in a specific manner is called equation of state. A thermodynamic equilibrium is completely specified by pressure, volume, temperature state variables by the equation of state. If the system is not in thermodynamic equilibrium, then these equations cannot specify the state of the system.

92. Which of the following statement is correct?

An ideal gas obeys the equation PV = NkT at thermodynamic equilibrium.
Since all four macroscopic variables (P, V, T and N) are connected by this equation, we cannot change one variable alone
1 alone
2 alone
1, 2
None

Explanation

An ideal gas obeys the equation PV = NkT at thermodynamic equilibrium. Since all four macroscopic variables (P, V, T and N) are connected by this equation, we cannot change one variable alone. For example, if we push the piston of a gas container, the volume of the gas will decrease but pressure will increase or if heat is supplied to the gas, its temperature will increase, pressure and volume of the gas may also increase.

93. Which of the following statement is correct?

There is another example of equation of state called van der Waals equation.
The air molecules in the room truly obey van der Waals equation of state.
1 alone
2 alone
1, 2
None

Explanation

There is another example of equation of state called van der Waals equation. Real gases obey this equation at thermodynamic equilibrium. The air molecules in the room truly obey van der Waals equation of state. But at room temperature with low density we can approximate it into an ideal gas.

94. Which of the following statement is incorrect?

The zeroth law of thermodynamics states thermal equilibrium between systems
It states that if two systems, A and B, are in thermal equilibrium with a third system, C, then A and B are in thermal equilibrium with each other
1 alone
2 alone
1, 2
None

Explanation

The zeroth law of thermodynamics states that if two systems, A and B, are in thermal equilibrium with a third system, C, then A and B are in thermal equilibrium with each other.

95.____ is the property which determines whether the system is in thermal equilibrium with other

systems or not.

Temperature
Pressure
Volume
None

Explanation

Temperature is the property which determines whether the system is in thermal equilibrium with other systems or not. Zeroth law enables us to determine the temperature.

96. ______ principle is used in finding the body temperature

Zeroth law of thermodynamics
Newtons 1^st law
Newtons 3^rd law
None

Explanation

Zeroth law enables us to determine the temperature. For example, when a thermometer is kept in contact with a human body, it reaches thermal equilibrium with the body. At this condition, the temperature of the thermometer will be same as the human body. This principle is used in finding the body temperature.

97. The internal energy of a thermodynamic system is_______

Kinetic energy alone
Potential energy of all the molecules
Both a and b
None

Explanation

The internal energy of a thermodynamic system is the sum of kinetic and potential energies of all the molecules of the system with respect to the centre of mass of the system.

98. The energy due to molecular interaction is called_______

Internal potential energy
Internal kinetic energy
External potential energy
External kinetic energy

Explanation

The energy due to molecular interaction is called internal potential energy (EP). Example: Bond energy.

99. Which of the following are included in internal kinetic energy?

Rotational motion
Translational motion
Vibrational motion
1, 2
1, 3
2, 3
All the above

Explanation

The energy due to molecular motion including translational, rotational and vibrational motion is called internal kinetic energy (E_K).

100. Which of the following statement is correct?

Internal energy is a state variable
It depends only on the initial state of the thermodynamic system
1 alone
2 alone
1, 2
None

Explanation

Internal energy is a state variable. It depends only on the initial and final states of the thermodynamic system. For example, if the temperature of water is raised from 30°C to 40°C either by heating or by stirring, the final internal energy depends only on the final temperature 40°C and not the way it is arrived at.

101. Which of the following statement is incorrect?

It is very important to note that the internal energy of a thermodynamic system is associated with only the kinetic energy of the individual molecule
The bulk kinetic energy of the entire system or gravitational potential energy of the system should not be mistaken as a part of internal energy
1 alone
2 alone
1, 2
None

Explanation

It is very important to note that the internal energy of a thermodynamic system is associated with only the kinetic energy of the individual molecule due to its random motion and the potential energy of molecules which depends on their chemical nature. The bulk kinetic energy of the entire system or gravitational potential energy of the system should not be mistaken as a part of internal energy.

102. Which of the following statement is correct?

It is to be noted that heat does not always increases the internal energy
We can see that in ideal gases during isothermal process the internal energy will increase
1 alone
2 alone
1, 2
None

Explanation

It is to be noted that heat does not always increases the internal energy. Later we shall see that in ideal gases during isothermal process the internal energy will not increase even though heat flows in to the system.

103. Which of the following statement is correct?

The temperature of an object can be increased by heating it or by doing some work on it.
Due to the turning of wheel inside water, frictional force comes in between the water and the paddle wheel.
Friction will increase the heat
1, 2
1, 3
2, 3
All the above

Explanation

The temperature of an object can be increased by heating it or by doing some work on it. In the eighteenth century, James Prescott Joule showed that mechanical energy can be converted into internal energy and vice versa. In his experiment, two masses were attached with a rope and a paddle wheel as shown in Figure 8.19. When these masses fall through a distance h due to gravity, both the masses lose potential energy equal to 2mgh. When the masses fall, the paddle wheel turns. Due to the turning of wheel inside water, frictional force comes in between the water and the paddle wheel. This causes a rise in temperature of the water.

104. 1 Cal =_____

4.186 J
5.12 J
3.26 J
2.33 J

Explanation

In fact, Joule was able to show that the mechanical work has the same effect as giving heat. He found that to raise 1 g of an object by 1°C, 4.186 J of energy is required. In earlier days the heat was measured in calorie. 1 Cal = 4.186 J

105. A student had a breakfast of 200 food calories. He thinks of burning this energy by drawing water from the well and watering the trees in his school. Depth of the well is about 25 m. The pot

can hold 25L of water and each tree requires one pot of water. How many trees can he water?

6250 J
6650 J
3350 J
2235 J

Explanation

106. The first law of thermodynamics is a statement of______

Law of conservation of mass
Law of conservation of weight
Law of conservation of Energy
Law of conservation of pressure

Explanation

The first law of thermodynamics is a statement of the law of conservation of energy. In Newtonian mechanics conservation of energy involves kinetic and potential energies of bulk objects.

107. Match the following

Heat flows into the system 1. W is positive
Heat flows out of the system 2. W is negative
Work done on the system 3. Internal energy increases
Work done by the system 4. Internal energy decreases
2, 1, 4, 3
3, 4, 2, 1
3, 1, 2, 4
2, 1, 3, 4

Explanation

108. 1^st law of thermodynamics is applicable to____

Solid
Liquid
Gas
Universal

Explanation

Even though we often explain first law of thermodynamics using gases, this law is universal and applies to liquids and solids also.

109. A person does 30 kJ work on 2 kg of water by stirring using a paddle wheel. While stirring, around 5 kcal of heat is released from water through its container to the surface and surroundings by thermal conduction and radiation. What is the change in internal energy of the system?

9080 J
8090 J
1010 J
1000 J

Explanation

110. Jogging every day is good for health. Assume that when you jog a work of 500 kJ is done and

230 kJ of heat is given off. What is the change in internal energy of your body?

– 730 kJ
– 630 kJ
– 530 kJ
– 430 kJ

Explanation

111. A gas expands from volume 1m³ to 2m³ at constant atmospheric pressure. Calculate the work

done by the gas. (kJ)

101
120
230
111

Explanation

112. Which of the following has two specific heat capacity?

Solid
Liquid
Gas
All the above

Explanation

Specific heat capacity of a given system plays a very important role in determining the structure and molecular nature of the system. Unlike solids and liquids, gases have two specific heats: specific heat capacity at constant pressure (s_p) and specific heat capacity at constant volume (s_v).

113. Which of the following statement is correct?

The amount of heat energy required to raise the temperature of one kg of a substance by 1 K or 1°C by keeping the pressure constant is called specific heat capacity at constant pressure
When the heat energy is supplied to the gas, it contracts to keep the pressure constant
1 alone
2 alone
1, 2
None

Explanation

The amount of heat energy required to raise the temperature of one kg of a substance by 1 K or 1°C by keeping the pressure constant is called specific heat capacity of at constant pressure. When the heat energy is supplied to the gas, it expands to keep the pressure constant.

114. What work does the heat energy do when gas is heated under constant pressure?

Expansion of gas
Increase external energy of gas
Increase internal energy of gas
1, 2
1, 3
2, 3
All the above

Explanation

In this process of heating gas under constant pressure, a part of the heat energy is used for doing work (expansion) and the remaining part is used to increase the internal energy of the gas.

115. The amount of heat required to raise the temperature of one mole of a substance by 1K or 1°C at

constant volume is called_____ at constant pressure

Molar heat capacity
Specific heat capacity
Molar Specific heat capacity
None

Explanation

Sometimes it is useful to calculate the molar heat capacities Cp and C_v. The amount of heat required to raise the temperature of one mole of a substance by 1K or 1°C at constant volume is called molar specific heat capacity at constant volume (C_v). If pressure is kept constant, it is called molar specific heat capacity at constant pressure (C_p).

116. Which of the following statement about Meyer’s relation is correct?

It implies that the molar specific heat capacity of an ideal gas at constant pressure is greater than molar specific heat capacity at constant volume.
It implies that the molar specific heat capacity of an ideal gas at constant pressure is lesser than molar specific heat capacity at constant volume.
1 alone
2 alone
1, 2
None

Explanation

Meyer’s relation implies that the molar specific heat capacity of an ideal gas at constant pressure is greater than molar specific heat capacity at constant volume.

117. Which of the following is constant is Isothermal process?

Temperature
Pressure
Volume
All the above

Explanation

Isothermal process is a process in which the temperature remains constant but the pressure and volume of a thermodynamic system will change.

118. All biological processes occur at constant body temperature of____ ^oC

Explanation

When water is heated, at the boiling point, even when heat flows to water, the temperature will not increase unless the water completely evaporates. Similarly, at the freezing point, when the ice melts to water, the temperature of ice will not increase even when heat is supplied to ice. All biological processes occur at constant body temperature (37°C).

119. To calculate the work done in an isothermal process, we assume that the process is_____

Dynamic
Static
Quasi Static
None

Explanation

To calculate the work done in an isothermal process, we assume that the process is quasi-static. If it is not quasi-static, we cannot substitute P = µRT/V in equation.

120. A 0.5 mole of gas at temperature 300 K expands isothermally from initial volume of 2 L to 6 L. What is the work done by the gas?

3. 39 kJ
1.369 kJ
1.639 kJ
2.23 kJ

Explanation

121. A 0.5 mole of gas at temperature 300 K expands isothermally from an initial volume of 2 L to 6

L What is the final pressure of the gas? (The value of gas constant, R = 8.31 J mol^-1 K^-1)

210 k Pa
207.75 k Pa
220 k Pa
120 k Pa

Explanation

122. In which process no heat flows into or out of the system?

Adiabatic process
Abiastalic process
Isothermal process
Isomatic process

Explanation

Adiabatic process is a process in which no heat flows into or out of the system (Q=0). Where Q value will be Zero in the system.

123. Which of the following may change in adiabatic process?

Volume
Pressure
Temperature
1, 2
1, 3
2, 3
All the above

Explanation

In an Adiabatic process, the gas can expand by spending its internal energy or gas can be compressed through some external work. So, the pressure, volume and temperature of the system may change in an adiabatic process.

124. For an adiabatic process, the first law becomes_____

ΔU = 0
ΔU = −W
ΔU = W
ΔU = ΔV

Explanation

For an adiabatic process, the first law becomes ΔU = −W. This implies that the work is done by the gas at the expense of internal energy or work is done on the system which increases its internal energy.

125. When the warm air rises from the surface of the Earth, it_____

Expands
Contracts
Adiabatically expands
Adiabatically Contracts

Explanation

When the warm air rises from the surface of the Earth, it adiabatically expands. As a result, the water vapor cools and condenses into water droplets forming a cloud.

126. Which of the following statement is correct?

When the piston is compressed so quickly that there is no time to exchange heat to the surrounding, the temperature of the gas increases rapidly
This principle is used in the petrol engine
The air-gasoline mixer is compressed so quickly (adiabatic compression) that the temperature increases enormously, which is enough to produce a spark
1, 2
1, 3
2, 3
All the above

Explanation

When the piston is compressed so quickly that there is no time to exchange heat to the surrounding, the temperature of the gas increases rapidly. This is shown in the figure. This principle is used in the diesel engine. The air-gasoline mixer is compressed so quickly (adiabatic compression) that the temperature increases enormously, which is enough to produce a spark.

127. Which of the following is constant in Isobaric process?

Temperature
Pressure
Internal energy
Volume

Explanation

Isobaric process is a thermodynamic process that occurs at constant pressure. Even though pressure is constant in this process, temperature, volume and internal energy are not constant.

128. Most of the cooking processes in our kitchen are_____ process

Isothermal
Isobaric
Adiabatic
None

Explanation

Most of the cooking processes in our kitchen are isobaric processes. When the food is cooked in an open vessel, the pressure above the food is always at atmospheric pressure.

129. Which of the following is constant in Isochoric process?

Temperature
Pressure
Internal energy
Volume

Explanation

Isochoric process is a thermodynamic process in which the volume of the system is kept constant. But pressure, temperature and internal energy continue to be variables.

130. How many processes does petrol engine undergo?

Explanation

In automobiles the petrol engine undergoes four processes. First the piston is adiabatically compressed to some volume as shown. In the second process, the volume of the air-fuel mixture is kept constant and heat is being added. As a result, the temperature and pressure are increased. This is an isochoric process. For a third stroke there will be an adiabatic expansion, and fourth stroke again isochoric process by keeping the piston immoveable.

131. 500 g of water is heated from 30°C to 60°C. Ignoring the slight expansion of water, calculate the

change in internal energy of the water? (specific heat of water 4184 J/kg.K).

62.76 kJ
162.76 kJ
262.76 kJ
362.76 kJ

Explanation

132. Which of the following statement is correct?

When a hot object is in contact with a cold object, heat always flows from the hot object to cold object
Heat does not flow in reverse direction
In nature the direction of heat flow is always from higher temperature to lower temperature.
1, 2
1, 3
2, 3
All the above

Explanation

When a hot object is in contact with a cold object, heat always flows from the hot object to cold object but not in the reverse direction. According to first law, it is possible for the energy to flow from hot object to cold object or from cold object to hot object. But in nature the direction of heat flow is always from higher temperature to lower temperature.

133. When brakes are applied, work done against friction is converted into_____

Motion
Heat
Pressure
Cold

Explanation

When brakes are applied, a car stops due to friction and the work done against friction is converted into heat. But this heat is not reconverted to the kinetic energy of the car. So the first law is not sufficient to explain many of natural phenomena.

134. Which of the following are the conditions for reversible process?

The process should proceed at an extremely slow rate
The system should remain in mechanical, thermal and chemical equilibrium state at all the times with the surroundings, during the process.
No dissipative forces such as friction, viscosity, electrical resistance should be present
1, 2
1, 3
2, 3
All the above

Explanation

A quasi–static isothermal expansion of gas, slow compression and expansion of a spring.

Conditions for reversible process:

1. The process should proceed at an extremely slow rate.

2. The system should remain in mechanical, thermal and chemical equilibrium state at all the times with the surroundings, during the process.

3. No dissipative forces such as friction, viscosity, electrical resistance should be present.

135. Which of the following statement is correct?

All-natural processes are irreversible.
Irreversible process can be plotted in a PV diagram
1 alone
2 alone
1, 2
None

Explanation

All-natural processes are irreversible. Irreversible process cannot be plotted in a PV diagram, because these processes cannot have unique values of pressure, temperature at every stage of the process.

136. Which of the following statement is correct?

In the modern technological world, the role of automobile engines plays a vital role in for transportation.
In motor bikes and cars there are engines which take in petrol or diesel as input, and do work by rotating wheels
1 alone
2 alone
1, 2
None

Explanation

In the modern technological world, the role of automobile engines plays a vital role in for transportation. In motor bikes and cars there are engines which take in petrol or diesel as input, and do work by rotating wheels.

137. Most of these automobile engines have efficiency not greater than____ %

Explanation

Most of these automobile engines have efficiency not greater than 40%. The second law of thermodynamics puts a fundamental restriction on efficiency of engines. Therefore, understanding heat engines is very important.

138. ______ is defined as a thermodynamic system which has very large heat capacity

Water tank
Reservoir
Hot water in tumbler
All the above

Explanation

Reservoir is defined as a thermodynamic system which has very large heat capacity. By taking in heat from reservoir or giving heat to reservoir, the reservoir’s temperature does not change.

139. How many parts are there in heat engine?

Explanation

Heat engine is a device which takes heat as input and converts this heat in to work by undergoing a cyclic process. A heat engine has three parts: (a) Hot reservoir (b) Working substance (c) Cold reservoir.

140. Which of the following statement is correct?

The heat engine works in a cyclic process.
After a cyclic process it returns to the same state
The change in the internal energy of the heat engine is infinity
1, 2
1, 3
2, 3
All the above

Explanation

The heat engine works in a cyclic process. After a cyclic process it returns to the same state. Since the heat engine returns to the same state after it ejects heat, the change in the internal energy of the heat engine is zero

141. Which of the following statement about Kelvin Planck statement is correct?

It is impossible to construct a heat engine that operates in a cycle, whose sole effect is to convert the heat completely into work
This implies that no heat engine in the universe can have 100% efficiency.
1 alone
2 alone
1, 2
None

Explanation

Kelvin-Planck statement:

It is impossible to construct a heat engine that operates in a cycle, whose sole effect is to convert the heat completely into work. This implies that no heat engine in the universe can have 100% efficiency.

142. Which of the following statement is correct?

According to first law of thermodynamics, in an isothermal process the given heat is completely converted into work
For non-cyclic process like an isothermal expansion, the heat can be completely converted into work.
1 alone
2 alone
1, 2
None

Explanation

143. During a cyclic process, a heat engine absorbs 500 J of heat from a hot reservoir, does work and

ejects an amount of heat 300 J into the surroundings (cold reservoir). Calculate the efficiency of

the heat engine?

0.4
0.6
0.9
0.7

Explanation

144. Who proved that a certain reversible engine operated in cycle between hot and cold reservoir can have maximum efficiency?

James Carnot
James Princep
James Krikup
James Cameron

Explanation

In the year 1824 a young French engineer Sadi Carnot proved that a certain reversible engine operated in cycle between hot and cold reservoir can have maximum efficiency. This engine is called Carnot engine.

145. A steam engine boiler is maintained at 250°C and water is converted into steam. This steam is

used to do work and heat is ejected to the surrounding air at temperature 300K. Calculate the

maximum efficiency it can have?

0.3
0.23
0.43
0.65

Explanation

146. There are two Carnot engines A and B operating in two different temperature regions. For Engine A the temperatures of the two reservoirs are 150°C and 100°C. For engine B the temperatures of the reservoirs are 350°C and 300°C. What is engine A efficiency?

0.11
0.43
0.23
0.34

Explanation

147. Which of the following statement is correct?

Diesel engines used in cars and petrol engines used in our motor bikes are all real heat engines
The efficiency of diesel engines has maximum up to 44% and the efficiency of petrol engines are maximum up to 30%.
1 alone
2 alone
1, 2
None

Explanation

Diesel engines used in cars and petrol engines used in our motor bikes are all real heat engines. The efficiency of diesel engines has maximum up to 44% and the efficiency of petrol engines are maximum up to 30%. Since these engines are not ideal heat engines (Carnot engine), their efficiency is limited by the second law of thermodynamics.

148. _____ is also called ‘measure of disorder’.

Entropy
Enthalpy
Endom
None

Explanation

Entropy is also called ‘measure of disorder’. All- natural process occurs such that the disorder should always increases.

149. A refrigerator has COP of 3. How much work must be supplied to the refrigerator in order to

remove 200 J of heat from its interion?

66.67 J
66.67 kJ
56.67 J
56. 67 kJ

Explanation

150. Top of the atmosphere is at___ °C and bottom of the atmosphere is at__ °C

-19, 14
19, 14
19, -14
-19, -14

Explanation

The presence of atmosphere in the earth plays very important role in human lives. Top of the atmosphere is at -19°C and bottom of the atmosphere is at +14°C. The increase in 33°C from top to bottom is due to some gases present in the atmosphere. These gases are called Greenhouse gases and this effect is called Greenhouse effect.

151. Which of the following are green-house gases?

Ne
He
CO₂
All the above

Explanation

The greenhouse gases are mainly CO₂, water vapour, Ne, He, NO₂, CH4, Xe, Kr, ozone and NH₃. Except CO₂ and water vapor, all others are present only in very small amount in the atmosphere.

152. CO2 and other gases in the atmosphere trap____ radiation, keeping the earth warm.

UV
IR
X- ray
All the above

Explanation

11th Science Lesson 7 Questions in English

7] Environmental Chemistry

1. Who was awarded the Nobel Prize for the development of new chemicals based on Green chemistry in 2005?

a) Yuves Chauvin

b) Robert H.Grubbs

c) R. Schrock

d) All the above

Explanation

The Nobel Prize in chemistry 2005 was awarded jointly to Yves Chauvin, Robert H. Grubbs and Richard R. Schrock for the development of new chemicals based on Green chemistry.

2. Choose the Incorrect statements.

i) Yves Chauvin explained the types of metal compound catalysts in reactions in the year 1971.

ii) Richard Schrock was one of the people to produce efficient metal compound catalysts for metathesis.

iii) Robert Grubbs developed better catalysts that are stable in air.

a) i only

b) ii only

c) iii only

d) All the above

Explanation

In 1971 Yves Chauvin explained the types of metal compound that act as catalysts in the reactions. Richard Schrock was the first to produce efficient metal compound catalysts for metathesis in 1990. Two years later Robert Grubbs developed better catalysts, stable in air that was highlighted in many applications.

3. Which of the following are the main objectives of the environmental chemistry?

a) Deals with the study of chemicals and processes occurring in the environment by human activities.

b) Deals with sources, causes and methods of Pollution.

c) Deals with all types of pollution like air, water and soil.

d) All the above

Explanation

Environmental chemistry is a branch of chemistry which deals with the study of chemicals and chemical processes occurring in the environment by direct human activities. It also deals with sources, causes and methods of controlling air, water and soil pollution.

4. Assertion (A): All the substances causes pollution of environment are called as pollutants.

Reasoning(R): The Pollutants may be solid, liquids or gaseous substances.

a) Both A and R is True and R is the correct explanation of A.

b) Both A and R is True but R is not the correct explanation of A.

c) A is True but R is False.

d) Both A and R is False.

Explanation

Environmental pollution is usually caused by the addition of waste products of human activity to the environment. The substances which cause pollution of environment are called pollutants. The pollutants may be solids, liquids or gaseous substances present in significant concentration in the environment.

5. Which of the following is not a bio-degradable pollutant?

a) Plant wastes

b) Nuclear wastes

c) Animal wastes

d) Biological wastes

Explanation

Bio-degradable pollutants: The pollutants which can be easily decomposed by the natural biological processes are called bio-degradable pollutants. Examples: plant wastes, animal wastes etc.

6. Choose the incorrect statements.

i) Non bio-degradable pollutants cannot be decomposed by the natural biological process.

ii) In low concentration non bio-degradable pollutants are not harmful to living organisms.

iii) Metal wastes, DDT, plastics and nuclear wastes are some of the Non bio-degradable pollutants.

a) i only

b) ii only

c) iii only

d) None of the above

Explanation

Non bio-degradable pollutants: The pollutants which cannot be decomposed by the natural biological processes are called non bio-degradable pollutants. Examples: metal wastes (mainly Hg and Pb), D.D.T, plastics, nuclear wastes etc., these pollutants are harmful to living organisms even in low concentration. As they are not degraded naturally, it is difficult to eliminate them from our environment.

7. Which of the following is not included in the mixture of air?

a) Nitrogen

b) Argon

c) Water vapor

d) Helium

Explanation

Earth’s atmosphere is a layer of gases retained by the earth’s gravity. It contains roughly 78% nitrogen, 21% oxygen, 0.93% argon, 0.04% carbon dioxide, trace amounts of other gases and little amount of water vapor. This mixture is commonly known as air.

8. Which of this region is also known as ozonosphere?

a) Hydrosphere

b) Stratosphere

c) Mesosphere

d) Thermosphere

9. Identify the Incorrect match.

A. Stratosphere i) O₃

B. Thermosphere ii) NO⁺

C. Mesosphere iii) e^–

a) i only

b) ii only

c) iii only

d) None of the above

10. Which of the region is located between 85-100 km from the earth’s surface?

a) Ozonosphere

b) Thermosphere

c) Mesosphere

d) Ionosphere

Explanation

Regions of atmosphere

11. Which of this layer has about 80% mass of the atmosphere?

a) Troposphere

b) Stratosphere

c) Mesosphere

d) Exosphere

Explanation

Troposphere: The lowest layer of the atmosphere is called the troposphere and it extends from 0 – 10 km from the earth surface. About 80% of the mass of the atmosphere is in this layer.

12. Which of the following is not a category of troposphere?

a) Hydrosphere

b) Mesosphere

c) Lithosphere

d) Biosphere

Explanation

This troposphere is further divided as Hydrosphere, Lithosphere and Biosphere.

13. Which of this living organism are included in the biosphere of the Earth?

a) Lithosphere only

b) Hydrosphere only

c) Atmosphere only

d) All the above

Explanation

Biosphere: It includes the lithosphere hydrosphere and atmosphere integrating the living organism present in the lithosphere, hydrosphere and atmosphere.

14. Assertion (A): The Earth is called as a blue planet as 75% of earth’s surface is covered by water.

Reasoning(R): Hydrosphere only includes the fresh water sources of the Earth.

a) Both A and R is True and R is the correct explanation of A.

b) Both A and R is True but R is not the correct explanation of A.

c) A is True but R is False.

d) Both A and R is False.

Explanation

Hydrosphere: Hydrosphere includes all types of water sources like oceans, seas, rivers, lakes, streams, underground water, polar icecaps, clouds etc. It covers about 75% of the earth’s surface. Hence the earth is called as a blue planet.

15. In ____ an explosion at the Union Carbide pesticide plant released a cloud of toxic gas _____ into the air.

a) 1972, Ethyl alcohol

b) 1984, Methyl isocyanate

c) 1966, Benzene

d) 1989, Methane

Explanation

The world’s worst chemical disaster happened in the Indian city of Bhopal in the early morning hours of December 3, 1984. An explosion at the Union Carbide pesticide plant released a cloud of toxic gas (methyl isocyanate) CH3NCO into the air.

16. Which of this pollution is also studied as atmospheric pollution?

a) Lithospheric pollution

b) Hydrosphere pollution

c) Tropospheric pollution

d) Exospheric pollution

Explanation

Atmospheric pollution is generally studied as tropospheric pollution. Different types of atmospheric pollutions are Air pollution, Water pollution and Soil pollution.

17. Choose the incorrect statements.

i) Air pollution is caused by any undesirable change in air which adversely affects the living organisms.

ii) Air pollution is not limited to any of the regions of the atmosphere.

iii) Air pollution is due to the excessive discharge of undesirable foreign matters in the atmosphere.

a) i only

b) ii only

c) iii only

d) None of the above

Explanation

Air pollution: Any undesirable change in air which adversely affects living organisms is called air pollution. Air pollution is limited to troposphere and stratosphere. Air pollution is mainly due to the excessive discharge of undesirable foreign matter in to the atmospheric air.

18. Which of the following is not a gaseous air pollutant?

a) Oxides of nitrogen

b) Oxides of metals

c) Oxides of carbon

d) Hydrocarbons

Explanation

Air pollutants may exist in two major forms namely, gases and particulates. Oxides of sulphur, oxides of nitrogen, oxides of carbon, and hydrocarbons are the gaseous air pollutants.

19. What are the harmful effects of the sulphur dioxide?

a) Eye irritation

b) Asthma

c) Bronchitis

d) All the above

Explanation

Sulphur dioxide and sulphur trioxide are produced by burning sulphur containing fossil fuels and roasting Sulphide ores. Sulphur dioxide is a poisonous gas to both animals and plants. Sulphur dioxide causes eye irritation, coughing and respiratory diseases like asthma, bronchitis, etc.

20. Assertion (A): Sulphur trioxide combines with water vapor and forms H₂SO₄ and comes down as Acid rain.

Reasoning(R): Sulphur dioxide is oxidized into SO₃ in the presence of particulate matter in the polluted air.

a) Both A and R is True and R is the correct explanation of A.

b) Both A and R is True but R is not the correct explanation of A.

c) A is True but R is False.

d) Both A and R is False.

Explanation

Sulphur dioxide is oxidized into more harmful sulphur trioxide in the presence of particulate matter present in polluted air .SO₃ combines with atmospheric water vapor to form H₂SO₄ which comes down in the form of acid rain.

21. Which of the following is not true about the effects of nitrogen oxide?

a) The oxides of nitrogen are converted into nitric acid and form the acid rain.

b) The oxides of nitrogen form reddish brown haze in heavy traffic.

c) Nitrogen dioxide does not affect the plants.

d) Nitrogen oxide is a respiratory irritant and causes asthma and lung injury.

Explanation

The oxides of nitrogen are converted into nitric acid which comes down in the form of acid rain. They also form reddish brown haze in heavy traffic. Nitrogen dioxide potentially damages plant leaves and retards photosynthesis. NO2 is a respiratory irritant and it can cause asthma and lung injury. Nitrogen dioxide is also harmful to various textile fibres and metals.

22. Which of these produces the carbon monoxide?

a) Incomplete combustion of coal

b) Automobile exhaust

c) Incomplete combustion of firewood

d) All the above

Explanation

Carbon monoxide is a poisonous gas produced as a result of incomplete combustion of coal or firewood. It is released into the air mainly by automobile exhaust.

23. Which of these are the effects of carbon monoxide in blood circulation?

a) Cardiac arrest

b) Dizziness

c) Loss of consciousness

d) All the above

Explanation

Carbon monoxide binds with hemoglobin Unit and forms carboxy hemoglobin which impairs normal oxygen transport by blood and hence the oxygen carrying capacity of blood is reduced. This oxygen deficiency results in headache, dizziness, tension, Loss of consciousness, blurring of eye sight and cardiac arrest.

24. Choose the Incorrect statements.

i) Carbon dioxide is released into the atmosphere mainly by the process of respiration.

ii) Green plants can convert CO₂ gas in the atmosphere into carbohydrate and oxygen through a process called photosynthesis.

iii) The decreased CO₂ level in the atmosphere is responsible for global warming. It causes headache and nausea.

a) i only

b) ii only

c) iii only

d) None of the above

Explanation

Carbon dioxide is released into the atmosphere mainly by the process of respiration, burning of fossil fuels, forest fire, decomposition of limestone in cement industry etc. Green plants can convert CO2 gas in the atmosphere into carbohydrate and oxygen through a process called photosynthesis. The increased CO2 level in the atmosphere is responsible for global warming. It causes headache and nausea.

25. Choose the correct statements.

i) Hydrocarbons are the compounds composed of carbon with any gas or metal compounds.

ii) Hydrocarbons are the potential cancer causing agents.

a) i only

b) ii only

c) Both i and ii

d) Neither i nor ii

Explanation

The compounds composed of carbon and hydrogen only are called hydrocarbons. They are mainly produced naturally (marsh gas) and also by incomplete combustion of automobile fuel. They are potential cancer causing (carcinogenic) agents. For example, poly nuclear aromatic hydrocarbons (PAH) are carcinogenic they cause irritation in eyes and mucous membranes.

26. Who coined the term the Greenhouse Effect?

a) Jean Baptiste

b) Richard Schrock

c) Albert Einstein

d) Robert Grubbs

Explanation

In 1987, Jean Baptiste Fourier a French mathematician and scientist coined the term “Greenhouse Effect” for trapping of heat in the atmosphere by certain gases.

27. Which of these used to trap the heat in the atmosphere?

a) CFC

b) CH₄

c) CO₂

d) All the above

Explanation

The earth’s atmosphere allows most of the visible light from the Sun to pass through and reach Earth’s surface. As Earth’s surface is heated by sunlight, it radiates part of this energy back toward space as longer wavelengths (IR). Some of the heat is trapped by CH4, CO2, CFCs and water vapor present in the atmosphere. They absorb IR radiation and effectively block a large portion of earth’s emitted radiation. The radiation thus absorbed is partly reemitted to earth’s surface. Therefore, the earth’s surface gets heated up by a phenomenon called greenhouse effect.

28. Assertion (A): Global warming is the process of heating up the earth through the greenhouse effect.

Reasoning(R): The Carbon dioxide layer in the atmosphere reflects the infrared radiations and heat up the earth’s surface.

a) Both A and R is True and R is the correct explanation of A.

b) Both A and R is True but R is not the correct explanation of A.

c) A is True but R is False.

d) Both A and R is False.

Explanation

Thus Greenhouse effect may be defined as the heating up of the earth surface due to trapping of infrared radiations reflected by earth’s surface by CO₂ layer in the atmosphere”. The heating up of earth through the greenhouse effect is called global warming.

29. What will be the average surface temperature of the Earth without the greenhouse effect?

a) 0°F

b) 273°C

c) 1000°F

d) -10°C

Explanation

Without the heating caused by the greenhouse effect, Earth’s average surface temperature would be only about −18 °C (0 °F).

30. What is the pH value of the normal rain water?

a) 5.6

b) 50.2

c) 6.5

d) 6.6

Explanation

Rain water normally has a pH of 5.6 due to dissolution of atmospheric CO2 into it.

31. Which of these drops the pH of the rain water?

a) Sulphur Oxide

b) Hydrogen Sulphide

c) Nitrogen Oxide

d) Both a and c

Explanation

Oxides of sulphur and nitrogen in the atmosphere may be absorbed by droplets of water that make up clouds and get chemically converted into Sulphuric acid and nitric acid respectively. As a result, pH of rain water drops below the level 5.6, hence it is called acid rain.

32. Which of these react with the oxides of sulphur and nitrogen to produce acid rain?

a) Oxygen

b) Carbon dioxide

c) Hydrogen

d) Helium

Explanation

Acid rain is a by-product of a variety of sulphur and nitrogen oxides in the atmosphere. Burning of fossil fuels (coal and oil) in power stations, furnaces and petrol, diesel in motor engines produce sulphur dioxide and nitrogen oxides. The main contributors of acid rain are SO₂ and NO₂. They are converted into Sulphuric acid and nitric acid respectively by the reaction with oxygen and water.

33. Which of these is referred as stone leprosy?

a) Respiratory ailments in humans.

b) Acid rain effects in aquatic ecosystem.

c) Acid rain attacks on marbles.

d) Toxic effects of acid rain in water pipes.

Explanation

Acid rain causes extensive damage to buildings and structural materials of marbles. This attack on marble is termed as Stone leprosy.

CaCO₃ + H₂SO4→ CaSO4 + H₂O +CO₂↑

34. Choose the correct statements.

i) Particulate pollutants are large solid, gas and liquid particles.

ii) Dust, smoke and aerosols are some of the particulate pollutants.

iii) Most of the particulate pollutants are not hazardous.

a) i only

b) ii only

c) iii only

d) All the above

Explanation

Particulate pollutants are small solid particles and liquid droplets suspended in air. Many of particulate pollutants are hazardous. Examples: dust, pollen, smoke, soot and liquid droplets (aerosols) etc. Combustion of high ash fossil fuels creates fly ash and finishing of metals throws metallic particles into the atmosphere.

35. In which of these ways the particulate pollutants are generated?

a) Volcanic eruption

b) Dust blows

c) Incomplete combustion of fossil fuels

d) All the above

Explanation

The dust, pollen, smoke, soot and liquid droplets (aerosols) etc. are some examples of particulate pollutants. They are blown into the atmosphere by volcanic eruption, blowing of dust; incomplete combustion of fossil fuels induces soot.

36. Which of these are not viable particulates?

a) Bacteria

b) Soot

c) Moulds

d) Algae

Explanation

Viable particulates: The viable particulates are the small size living organisms such as bacteria, fungi, moulds, algae, etc. which are dispersed in air. Some of the fungi cause allergy in human beings and diseases in plants.

37. What are the functions of the non-viable particles?

a) Transportation of viable particulates.

b) Increase the size of viable particulates.

c) Creating new types of diseases in plants.

d) Reduce the number of viable particulates.

Explanation

Non-viable particulates: The non- viable particulates are small solid particles and liquid droplets suspended in air. They help in the transportation of viable particles.

38. How many types of nonviable particulates are classified?

a) 5

b) 7

c) 4

d) 2

Explanation

There are four types of nonviable particulates in the atmosphere. They are classified according to their nature and size.

39. Which of this combustion produce the particles or mixtures?

a) Metals

b) Organic matters

c) Biodegradable products

d) Inorganic matters

Explanation

The Particles (or) mixture of solid and liquid particles are formed by combustion of organic matter. For example, cigarette smoke, oil smoke, smokes from burning of fossil fuel , garbage and dry leaves.

40. Which of the following is not a dust form?

a) Sand blast

b) Cement factories dust

c) Fly ash

d) Pesticides spray

Explanation

Dust: Dust composed of fine solid particles produced during crushing and grinding of solid materials. For example, sand from sand blasting, saw dust from wood works, cement dust from cement factories and fly ash from power generating units.

41. Which of these forms create the mists?

a) Fine solid particles by grinding of solid materials.

b) Saw dust from wood works.

c) Spray liquids and condensation of vapors in air.

d) None of the above

Explanation

Mists: They are formed by particles of spray liquids and condensation of vapors in air. For example, Sulphuric acid mist, herbicides and insecticides sprays can form mists.

42. Which of this condensation of vapors creates fumes?

a) Sublimation

b) Distillation

c) Calcination

d) All the above

Explanation

Fumes: Fumes are obtained by condensation of vapors released during sublimation, distillation, boiling and calcination and by several other chemical reactions. For example, organic solvents, metals and metallic oxides form fume particles.

43. Which pollutants are responsible causes of pneumoconiosis?

a) Dust

b) Mist

c) Fumes

d) All the above

Explanation

Dust, mist, fumes, etc., are air borne particles which are dangerous for human health. Particulate pollutants bigger than 5 microns are likely to settle in the nasal passage whereas particles of about 10 micron enter the lungs easily and cause scaring or fibrosis of lung lining. They irritate the lungs and causes cancer and asthma. This disease is also called pneumoconiosis. Coal miners may suffer from black lung disease. Textile workers may suffer from white lung disease.

44. Which of this process removes the particulates from the air?

a) Electrostatic precipitators

b) Gravity settling chambers

c) Wet scrubbers

d) All the above

Explanation

The particulates from air can be removed by using electrostatic precipitators, gravity settling chambers, and wet scrubbers or by cyclone collectors. These techniques are based on washing away or settling of the particulates.

45. What is the main component of smog?

a) Smoke and fog

b) Metals and oxides

c) Hydrocarbons

d) Inorganic matters

Explanation

Smog is a combination of smoke and fog which forms droplets that remain suspended in the air. Smog is a chemical mixture of gases that forms a brownish yellow haze over urban cities.

46. Which of these causes the classical smog?

a) Photo chemical oxidants

b) Coal smoke

c) Saw dust

d) All the above

Explanation

There are two types of smog. One is Classical smog caused by coal smoke and fog second one is photo chemical smog caused by photo chemical oxidants.

47. In which year the London smog was first observed?

a) 1952

b) 1973

c) 1942

d) 1969

Explanation

Classical smog or London smog: Classical smog was first observed in London in December 1952 and hence it is also known as London Smog.

48. Which of the following is not true regarding the London smog?

a) It consists of smoke and fog and occurs in cool humid climates.

b) Its chemical composition is the mixture of SO₂, SO₃ and humidity.

c) It generally starts in midnight and becomes worse in early mornings.

d) It is also known as reducing smog.

Explanation

London smog consists of coal smoke and fog. It occurs in cool humid climate. This atmospheric smog found in many large cities. The chemical composition is the mixture of SO2, SO3 and humidity. It generally occurs in the morning and becomes worse when the sun rises. This is mainly due to the induced oxidation of SO2 to SO3, which reacts with water yielding sulphuric acid aerosol. Chemically it is reducing in nature because of high concentration of SO2 and so it is also called as reducing smog.

49. What are the effects of classical smog?

a) Acid rain

b) Poor visibility in traffics

c) Bronchial irritation

d) All the above

Explanation

Effects of classical smog: Smog is primarily responsible for acid rain. Smog results in poor visibility and it affects air and road transport. It also causes bronchial irritation.

50. Which type of smog is formed with the presence of sunlight?

a) Photo chemical smog

b) Classical fog

c) Mists

d) Reducing smog

Explanation

Photo chemical smog or Los Angel Smog: Photo Chemical smog was first observed in Los Angeles in 1950. It occurs in warm, dry and sunny climate. This type of smog is formed by the combination of smoke, dust and fog with air pollutants like oxides of nitrogen and hydrocarbons in the presence of sunlight. It forms when the sun shines and becomes worse in the afternoon.

51. Which of these results in the high oxidizing nature of the photo chemical smog?

a) NO₄ and O

b) NO and O

c) NO₂ and O₃

d) NO and O₂

Explanation

Chemically the photo chemical smog is oxidizing in nature because of high concentration of oxidizing agents NO₂ and O₃, so it is also called as oxidizing smog.

52. Which of these results in the reaction of un-burnt hydrocarbons with strong oxidizing agents?

a) Formaldehyde

b) Acrolein

c) Peroxy acetyl nitrate

d) All the above

Explanation

NO and O3 are strong oxidizing agent and can react with un burnt hydrocarbons in polluted air to form formaldehyde, Acrolein and peroxy acetyl nitrate (PAN).

53. What are the main components of Los Angeles smog?

a) Nitrogen oxide

b) Oxidized Hydrocarbon

c) Ozone

d) All the above

Explanation

The three main components of photo chemical smog are nitrogen oxide, ozone and oxidized hydro carbon like formaldehyde(HCHO), Acrolein (CH2=CH-CHO),peroxy acetyl nitrate (PAN).

54. Which of the following is not an direct effect of the photo chemical smog?

a) Irritation to skin, eye and throat.

b) Bronzing and glazing of young leaves.

c) Acid rain.

d) Corrosion in metal stones and painted surfaces.

Explanation

Photochemical smog causes irritation to eyes, skin and lungs, increase in chances of asthma. High concentrations of ozone and NO can cause nose and throat irritation, chest pain, uncomfortable in breathing etc. PAN is toxic to plants, attacks younger leaves and cause bronzing and glazing of their surfaces. It causes corrosion of metals stones, building materials and painted surfaces.

55. Which of this suppression will reduce the formation of photochemical smog?

a) Ozone

b) Hydrocarbons

c) Nitrogen oxides

d) Both b and c

Explanation

The formation of photochemical smog can be suppressed by preventing the release of nitrogen oxides and hydrocarbons into the atmosphere from the motor vehicles by using catalytic convertors in engines.

56. Which of these trees are used to metabolize the effects of nitrogen oxides?

a) Pinus

b) Pyrus

c) Juniparus

d) All the above

Explanation

Plantation of certain trees like Pinus, Pyrus, Querus Vitus and juniparus can metabolize nitrogen oxide.

57. Which of these layers acts as a shield for UV radiations at high altitudes??

a) CO₂

b) O₃

c) NO

d) O₂

Explanation

At high altitudes to the atmosphere consists of a layer of ozone (O3) which acts as an umbrella or shield for harmful UV radiations. It protects us from harmful effect such as skin cancer. UV radiation can convert molecular oxygen into ozone.

58. Which gas is thermodynamically unstable and decomposes into molecular oxygen?

a) Carbon dioxide

b) Helium

c) Ozone

d) Nitrogen

Explanation

Ozone gas is thermodynamically unstable and readily decomposes to molecular oxygen.

59. Which gases are most responsible for the depletion of the ozone layer?

a) Nitric Acid

b) CFC

c) ODS

d) All the above

Explanation

In recent years, a gradual depletion of this protective ozone layer has been reported. Nitric oxide and CFC are found to be most responsible for depletion of ozone layer. Generally substances that cause depletion of ozone or make it thinner are called Ozone Depletion Substances abbreviated as ODS.

60. In which of these forms nitrogen oxides are introduced into the stratosphere?

a) Exhaust gas

b) Active gas

c) Zero temperature gas

d) Thermal equilibrium gas

Explanation

Nitrogen oxides introduced directly into the stratosphere by the supersonic jet aircraft engines in the form of exhaust gases. These oxides are also released by combustion of fossil fuels and nitrogen fertilizers.

61. What is the trade name of Chloro fluoro derivatives?

a) Meso

b) Zeros

c) Frenos

d) None of the above

Explanation

The Chloro fluoro derivatives of methane and ethane are referred by trade name Freons.

62. Which of the following is not a property of the Chloro fluoro carbon compounds?

a) Unstable

b) Non-toxic

c) Non-corrosive

d) Liquefiable

Explanation

The Chloro Fluoro Carbon compounds are stable, non-toxic, noncorrosive and non-inflammable, easily liquefiable and are used in refrigerators, air- conditioners and in the production of plastic foams.

63. The CFC breaks up into ______ free radical in the presence of ______.

a) Hydrogen, Humidity

b) Carbon, Water vapor

c) Chlorine, UV radiation

d) Sodium, IR radiation

Explanation

In the presence of UV radiation, CFC’s break up into chlorine free radical Chlorine radical is regenerated in the course of reaction. Due to this continuous attack of Cl˚ thinning of ozone layer takes place which leads to formation of ozone hole. It is estimated that for every reactive chlorine atom generated in the stratosphere 1, 00, 000 molecules of ozone are depleted.

64. Assertion (A): Any change in the equilibrium level of the ozone will adversely affect life in the biosphere

Reasoning(R): The regular natural process of formation and destruction of ozone never disturbs the equilibrium level of ozone in the stratosphere.

a) Both A and R is True and R is the correct explanation of A.

b) Both A and R is True but R is not the correct explanation of A.

c) A is True but R is False.

d) Both A and R is False.

Explanation

The formation and destruction of ozone is a regular natural process, which never disturbs the equilibrium level of ozone in the stratosphere. Any change in the equilibrium level of the ozone in the atmosphere will adversely affect life in the biosphere.

65. What are the negative impacts of ozone layer depletion?

a) More UV rays will reach earth surface.

b) Cause skin cancer and decreases immunity in human beings.

c) Affects the growth of phytoplankton as a result ocean food chain is disturbed.

d) All the above

Explanation

Depletion of ozone layer will allow more UV rays to reach the earth surface and layer would cause skin cancer and also decrease the immunity level in human beings. UV radiation affects plant proteins which lead to harmful mutation of cells. UV radiation affects the growth of phytoplankton; as a result ocean food chain is disturbed and even damages the fish productivity.

66. Which of the natural element is essential for life?

a) Air

b) Water

c) Land

d) Food

Explanation

Water is essential for life. Without water life would have been impossible. The slogan, ‘Save Water, Water will save you’ tell us the importance of water. Such slogans tell us to save water. Apart from saving water, maintaining its quality is also equally important.

67. Which of the following pollutant originates from both natural and human activities?

a) Water pollutant

b) Air pollutant

c) Land pollutant

d) Forest pollutant

Explanation

The water pollutants originate from both natural and human activities.

68. Assertion (A): Easily identified source of pollution is called as point source.

Reasoning(R): Non-point sources of water pollution are mining wastes, acid rain, agricultural runoff and construction sediments.

a) Both A and R is True and R is the correct explanation of A.

b) Both A and R is True but R is not the correct explanation of A.

c) A is True but R is False.

d) Both A and R is False.

Explanation

Easily identified source of place of pollution is called as point source. Example: municipal and industrial discharge pipes. Non-point source cannot be identified easily, example: agricultural runoff, mining wastes, acid rain, and storm-water drainage and construction sediments.

69. Match the pollutant and their sources.

A. Microorganisms i) Mining of uranium materials

B. Radioactive substances ii) Chemical fertilizers

C. Heat iii) Domestic sewage

D. Plant nutrients iv) Cooling purpose in Industries

a) ii, iv, i, iii

b) iv, ii, iii, i

c) iii, i, iv, ii

d) iv, i, iii, ii

70. Which of these pollutants is not related to agricultural acivities?

a) Plant nutrients

b) Radioactive substances

c) Pesticides

d) Sediments

Explanation

List of major water pollutants and their sources

71. Which of these microorganisms causes the microbiological diseases?

a) Bacteria

b) Viruses

c) Protozoa

d) All the above

Explanation

Microbiological (Pathogens) Disease causing microorganisms like bacteria, viruses and protozoa are most serious water pollutants. They come from domestic sewage and animal excreta. Fish and shellfish can become contaminated and people who eat them can become ill. Some serious diseases like polio and cholera are water borne diseases. Human excreta contain bacteria such as Escherichia coli and Streptococcus faecalis which cause gastrointestinal diseases.

72. Which of these organic excessive growth also causes the water pollution?.

a) Grass

b) Phytoplankton

c) Algae

d) Aquatic animals

Explanation

Organic matter such as leaves, grass, trash etc can also pollute water. Water pollution is caused by excessive phytoplankton growth within water.

73. Which of this process provides excess nutrients to the water bodies?

a) Eutrophication

b) Chlorination

c) Metamorphism

d) Hybridization

Explanation

Eutrophication is a process by which water bodies receive excess nutrients that stimulates excessive plant growth (algae other plant weeds). This enhanced plant growth in water bodies is called as algae bloom. The growth of algae in extreme abundance covers the water surface and reduces the oxygen concentration in water. Thus, bloom-infested water inhibits the growth of other living organisms in the water body. This process in which the nutrient rich water bodies support a dense plant population kills animal life by depriving it of oxygen and results in loss of biodiversity is known as eutrophication.

74. Choose the Incorrect statement about the BOD of drinking water.

i) The total amount of oxygen in milligrams consumed by microorganism in decomposing the waste for 5 days is called as BOD.

ii) The water for calculating BOD is at 20°C and the value is expressed in ppm.

iii) The BOD value of the clean water will be above 17 ppm whereas the contaminated water is below 5 ppm.

a) i only

b) ii only

c) iii only

d) None of the above

Explanation

The total amount of oxygen in milligrams consumed by microorganisms in decomposing the waste in one liters of water at 20°C for a period of 5 days is called biochemical oxygen demand (BOD) and its value is expressed in ppm. BOD is used as a measure of degree of water pollution. Clean water would have BOD value less than 5 ppm whereas highly polluted water has BOD value of 17 ppm or more.

75. Which of the following is used as an oxidizing agent in COD?

a) MN₂SO₄

b) K₂Cr₂O₇

c) H₂SO₄

d) HCL

Explanation

BOD measurement takes 5 days so another parameter called the Chemical Oxygen Demand (COD) is measured. Chemical oxygen demand (COD) is defined as the amount of oxygen required by the organic matter in a sample of water for its oxidation by a strong oxidizing agent like K₂Cr₂O₇ in acid medium for a period of 2 hrs.

76. Which of this metal pollutant of drinking water causes kidney damage to humans?

a) Sodium

b) Cadmium

c) Tin

d) Copper

Explanation

Harmful effects of chemical water pollutants: Cadmium and mercury can cause kidney damage.. Polychlorinated biphenyls (PCBs) causes skin diseases and are carcinogenic in nature.

77. In which year the standard characteristics for the drinking water were prescribed by BIS?

a) 1962

b) 1975

c) 1991

d) 1980

Explanation

Nowadays most of us hesitate to use natural water directly for drinking, because biological, physical or chemical impurities from different sources mix with surface water or ground water. Institutions like WHO (World Health Organization) at world level and BIS (Bureau of Indian Standards) and ICMR (ICMR: Indian Council of Medical Research) at national level have prescribed standards for quality of drinking water. Standard characteristics prescribed for deciding the quality of drinking water by BIS, in 1991

78. What is the desirable pH limit of drinking water?

a) 6.5 to 8.5

b) 4.5 to 6.5

c) 5.5 to 7.5

d) 6 to 10.5

79. Which of the following is a biological characteristic of the drinking water?

a) Hardness

b) Bacteria

c) Coliforms

d) Dissolved solids

80. Identify the incorrect match of the physico-chemical charaectristics and its desirable limit.

A. Nitrate i) 45ppm

B. Fluroide ii) 1ppm

C. Chloride iii) 250ppm

D. Sulphate iv) 500ppm

a) i only

b) ii only

c) iii only

d) iv only

Explanation

Standard characteristics of drinking water

81. Which of the following statement is not true regarding the fluorides?

a) The fluoride ion deficiency in drinking water causes tooth decay.

b) Non-soluble fluorides are added to decrease the fluoride ion concentration up to 1 ppm.

c) The fluoride ion makes the enamel on teeth much harder.

d) Fluoride ion concentration above 2ppm causes brown mottling of teeth.

Explanation

Fluoride ion deficiency in drinking water causes tooth decay. Water soluble fluorides are added to increase the fluoride ion concentration up to 1 ppm. The Fluoride ions make the enamel on teeth much harder by converting hydroxyapatite, [3(Ca3(PO4)2.Ca(OH)2], the enamel on the surface of the teeth, into much harder fluorapatite, [3(Ca3(PO4)2.CaF2]. However, Fluoride ion concentration above 2 ppm causes brown mottling of teeth. Excess fluoride causes damage to bone and teeth.

82. Which of these human organs are affected by lead contamination above 50 ppb in drinking water?

a) Liver

b) Kidney

c) Reproductive systems

d) All the above

Explanation

Drinking water containing lead contamination above 50ppb can cause damage to liver, kidney and reproductive systems

83. What are the effects of excessive concentration of sulphate level in drinking water?

a) Laxative effect

b) Cancer

c) Harmless

d) Bronchitis

Explanation

Sulphate: Moderate level of sulphate is harmless. The excessive concentration (>500ppm) of sulphates in drinking water causes laxative effect.

84. Which of this ppm value of a drinking water will cause blue baby syndrome in children?

a) < 165 ppm

b) > 45 ppm

c) < 1000 ppm

d) >= 100 ppm

Explanation

Nitrate: Use of drinking water having concentration of nitrate higher than 45 ppm may causes methemoglobinemia (blue baby syndrome) disease in children.

85. Choose the Incorrect statements.

i) Most of the salts are soluble in water and includes cations like calcium, magnesium, sodium, potassium and iron.

ii) The anions included in water are carbonate, bicarbonate, chloride, sulphate, phosphate and nitrate.

iii) The Total dissolved solids concentration lower than 500 ppm in a drinking water causes irritation in stomach and intestine.

a) i only

b) ii only

c) iii only

d) None of the above

Explanation

Total dissolved solids (TDS): Most of the salts are soluble in water. It includes cations like calcium, magnesium, sodium, potassium, iron and anions like carbonate, bicarbonate, chloride, sulphate, phosphate and nitrate. Use of drinking water having total dissolved solids concentration higher than 500 ppm causes possibilities of irritation in stomach and intestine.

86. Which of the following facts about the soil is not true?

a) Soil is a thick layer of organic materials that covers the earth’s rocky surface.

b) Soil constitutes the upper crust of the earth supporting the land, plants and animals.

c) Soil pollution is defined as the buildup of toxic compounds, radioactive materials and chemical salts.

d) Soil pollution affects the structure and fertility of soil, groundwater quality and food chain.

Explanation

Soil is a thin layer of organic and inorganic material that covers the earth’s rocky surface. Soil constitutes the upper crust of the earth, which supports land, plants and animals. Soil pollution is defined as the buildup of persistent toxic compounds, radioactive materials, chemical salts and disease causing agents in soils which have harmful effects on plant growth and animal health. Soil pollution affects the structure and fertility of soil, groundwater quality and food chain in biological ecosystem.

87. Choose the correct statements.

i) Plants obtain carbon, hydrogen and oxygen from air and water.

ii) Plants absorb the essential nutrients from the artificial fertilizers.

iii) The usage of phosphate fertilizers and NPK increase the yield of the soil.

a) i only

b) ii only

c) iii only

d) All the above

Explanation

Sources of soil pollution: Artificial fertilizers: Soil nutrients are useful for growth of plants. Plants obtains carbon, hydrogen and oxygen from air or water, whereas other essential nutrients like nitrogen, phosphorous, potassium, calcium, magnesium, sulphur are being absorbed from soil. To remove the deficiency of nutrients in soil, farmers add artificial fertilizers. Increased use of phosphate fertilizers or excess use of artificial fertilizers like NPK in soil, results in reduced yield in that soil.

88. Assertion (A): Pesticides are the chemicals used to kill or stop the growth of unwanted organisms.

Reasoning(R): Pesticides does not affect the human beings and animals.

a) Both A and R is True and R is the correct explanation of A.

b) Both A and R is True but R is not the correct explanation of A.

c) A is True but R is False.

d) Both A and R is False.

Explanation

Pesticides are the chemicals that are used to kill or stop the growth of unwanted organisms. But these pesticides can affect the health of human beings.

89. Which of the following is not an insecticide?

a) DDT

b) NPK

c) BHC

d) Aldrin

Explanation

Insecticides: Insecticides like DDT, BHC, Aldrin etc. can stay in soil for long period of time and are absorbed by soil. They contaminate root crops like carrot, radish, etc.

90. Which of these compounds are generally used as a fungicide?

a) Mercury

b) Gold

c) Hydrogen

d) Argon

Explanation

Fungicide: Organic mercury compounds are used as most common fungicide. They dissociate in soil to produce mercury which is highly toxic.

91. Choose the incorrect statements.

i) Herbicides are used to control unwanted plants known as weed killers.

ii) Sodium chlorate and Sodium arsenate are known herbicides.

iii) Herbicides are not toxic to animals and mammals.

a) i only

b) ii only

c) iii only

d) None of the above

Explanation

Herbicides: Herbicides are the chemical compounds used to control unwanted plants. They are otherwise known as weed killers. Example: sodium chlorate (NaClO3) and sodium arsenate (Na3AsO3). Most of the herbicides are toxic to mammals.

92. Which of these human activities causes the major soil pollution?

a) Agriculture

b) Construction works

c) Industrial activities

d) All the above

Explanation

Industrial activities have been the biggest contributor to the soil pollution especially the mining and manufacturing activities.

93. Which of these chemicals are not involved in the industrial toxic wastes?

a) Cyanides

b) Silver

c) Copper

d) Zinc

Explanation

Large number of toxic wastes is released from industries. Industrial wastes include cyanides, chromates, acids, alkalis, and metals like mercury, copper, zinc, cadmium and lead etc. These industrial wastes in the soil surface lie for a long time and make it unsuitable for use.

94. Which of these are the waste management techniques?

a) Recycling

b) Growing more trees

c) Vehicle emission control

d) All the above

Explanation

Waste management: Environmental pollution can be controlled by proper disposal of wastes. Recycling: a large amount of disposed waste material can be reused by recycling the waste, thus it reduces the land fill and converts waste into useful forms. Substitution of less toxic solvents for highly toxic ones used in certain industrial processes. Use of fuels with lower sulphur content (e.g., washed coal) Growing more trees. Control measures in vehicle emissions are adequate.

95. What is the primary focus of Green chemistry?

a) Plant trees and save the Environment.

b) Recycle the hazardous substances.

c) Produce eco-friendly compounds.

d) Organic compounds for industrial usage

Explanation

Green chemistry is a chemical philosophy encouraging the design of products and processes that reduce or eliminate the use and generation of hazardous substances. For this, scientists are trying to develop methods to produce eco-friendly compounds.

96. Which of these are used to dehydrogenation of ethyl benzene?

a) Fe₂O₃

b) MnSo₄

c) CH₆

d) CH₃COOH

Explanation

Traditional route: This method involves two steps. Carcinogenic benzene reacts with ethylene to form ethyl benzene. Then ethyl benzene on dehydrogenation using Fe₂O₃/ Al₂O₃ gives styrene. Greener route: To avoid carcinogenic benzene, greener route is to start with cheaper and environmentally safer xylenes.

97. Choose the incorrect statements.

i) Tetrachloroethylene used in dry cleaning of clothes pollutes the ground water.

ii) Liquefied CO₂ with suitable detergent is not harmful to the ground water.

iii) HO₂ is used for bleaching clothes for better results and utilizes less water.

a) i only

b) ii only

c) iii only

d) None of the above

Explanation

Dry cleaning of clothes: Solvents like tetrachloroethylene used in dry cleaning of clothes, pollute the ground water and are carcinogenic. In the place of tetrachloroethylene, liquefied CO₂ with suitable detergent is an alternate solvent used. Liquefied CO₂ is not harmful to the ground water. Now days H₂O₂ used for bleaching clothes in laundry, gives better results and utilizes less water.

98. What is used in the conventional method of paper bleaching?

a) Sulphide

b) Iodine

c) Chlorine

d) Magnesium

Explanation

Bleaching of paper: The Conventional method of bleaching was done with chlorine. Nowadays H₂O₂ can be used for bleaching paper in presence of catalyst.

99. Which of these products is prepared by one step oxidation of ethene?

a) Acetaldehyde

b) Ether

c) Benzene

d) Isopropyl alcohol

Explanation

Synthesis of chemicals: Acetaldehyde is now commercially prepared by one step oxidation of ethene in the presence of ionic catalyst in aqueous medium with 90% yield.

100. Which of the following is an alternate for the petrol in automobiles?

a) Ethanol

b) Hydrogen

c) Methanol

d) Hydrocarbons

Explanation

Instead of petrol, methanol is used as a fuel in automobiles..

101. How many categories of pollutants are classified?

a) 3

b) 4

c) 5

d) 2

Explanation

Environmental pollution is the effect of undesirable changes in the surrounding that have harmful effects on living things. Pollutants are generally classified as rapidly degradable (e.g. discarded vegetables) slowly degradable (e.g. Agriculture waste) and non-bio degradable pollutants (e.g. DDT, plastic materials).

102. Which of this pollution greatly affects the biosphere of the earth?

a) Stratosphere

b) Hydrosphere

c) Mesosphere

d) Exosphere

Explanation

Atmospheric pollutions include tropospheric and stratospheric pollution. Troposphere and stratosphere greatly affect the biosphere of the earth due to which the study of pollutions in these regions is most important.

103. Choose the Incorrect statements.

i) Troposphere is the highest region of atmosphere.

ii) Gaseous pollutants SO, NO, CO, O₃ hydrocarbons pollute the troposphere.

iii) The Particulate pollutants that pollute troposphere are dust, mist, fumes and smog.

a) i only

b) ii only

c) iii only

d) All the above

Explanation

Troposphere is the lowest region of atmosphere in which man, animal and plants exist. Gaseous pollutants like SOx, NOx, CO, CO₂, O₃ hydrocarbons and particulate pollutants like dust, mist, fumes, smog cause pollutions in troposphere.

104. Assertion (A): Acid rain results in the human activities that emit sulphur oxides and nitrogen oxides in the atmosphere.

Reasoning(R): If the PH value of rain water is lower than 5.6 then it is called as Acid rain.

a) Both A and R is True and R is the correct explanation of A.

b) Both A and R is True but R is not the correct explanation of A.

c) A is True but R is False.

d) Both A and R is False.

Explanation

Acid rain: When the PH of rain water becomes lower than 5.6 it is called acid rain. Acid rain is a byproduct of various human activities that emit sulphur oxides and nitrogen oxides in atmosphere. It damages buildings, statues and other monuments.

105. Which of the following is not included in the greenhouse gas?

a) O₂

b) N₂

c) CH₄

d) CFC

Explanation

The process of warming up of earth is known as greenhouse effect or global warming. CO₂, CH₄, O₃, CFC, N₂ and water vapor present in atmosphere act as a greenhouse gases.

106. Which of this greenhouse gas has the lowest heat retaining capacity?

a) CFC

b) N₂O

c) CO₂

d) CH₄

Explanation

Heat retaining capacity of greenhouse gases are called Global Warming Potential (GWP).The GWP based sequence of greenhouse gases is as CFC>N₂O>CH₄>CO₂.

107. Which of these humus cover is termed as soil?

a) Lithosphere

b) Troposphere

c) Exosphere

d) Mesosphere

Explanation

Lithosphere with humus cover is known as soil. The topsoil provides water and all nutrients required by plants for their growth.

108. Which of the following does not results in soil pollution?

a) Industrial waste

b) Organic wastes

c) Artificial fertilizers

d) Pesticides

Explanation

Industrial waste, artificial fertilizers and pesticides result in soil pollution.

109. Which of these methods are used for solid waste management?

a) Segregation

b) Dumping

c) Incineration

d) All the above

Explanation

The strategies for controlling environmental pollution are called can be waste management. Waste management involves reduction and proper disposal of waste. Wastes are produced in three forms, solid, liquid and gas. Solid waste can be disposed by segregation, dumping, incineration and composting.

110. Which of the following is majorly included in the earth’s atmosphere layer?

a) Nitrogen

b) Carbon dioxide

c) Hydrogen

d) Oxygen

Explanation

Earth’s atmosphere is a layer of gases retained by the earth’s gravity. It contains roughly 78% nitrogen, 21% oxygen, 0.93% argon, 0.04% carbon dioxide.

111. Which of these is not included in the lithosphere?

a) Mountains

b) Glaciers

c) Soil

d) Rocks

Explanation

Lithosphere includes soil, rocks and mountains which are solid components of earth.

112. How many types of major pollution are categorized?

a) 5

b) 10

c) 4

d) 3

Explanation

Different types of atmospheric pollutions are Air pollution, Water pollution and Soil pollution.

113. To which of these regions air pollution is limited?

a) Ionosphere

b) Mesosphere

c) Stratosphere

d) Exosphere

Explanation

Air pollution is limited to troposphere and stratosphere.

114. Choose the correct statements about oxides of sulphur.

i) Sulphur dioxide and sulphur trioxide are produced by burning fossil fuels and roasted sulphides ores.

ii) Sulphur dioxide is not harmful to plants.

a) i only

b) ii only

c) Both i and ii

d) Neither i nor ii

Explanation

Sulphur dioxide and sulphur trioxide are produced by burning sulphur containing fossil fuels and roasting Sulphide ores. Sulphur dioxide is a poisonous gas to both animals and plants.

115. Which of the following process produces the oxides of nitrogen?

a) Oxidation of nitrogen in air.

b) Burning fossil fuels

c) High temperature combustion

d) Both a and c

Explanation

Oxides of nitrogen are produced during high temperature combustion processes, oxidation of nitrogen in air and from the combustion of fuels coal, diesel, petrol.

116. Which process release the carbon dioxide into the atmosphere?

a) Burning fossils fuels

b) Decomposition of limestone

c) Respiration process

d) All the above

Explanation

Carbon dioxide is released into the atmosphere mainly by the process of respiration, burning of fossil fuels, forest fire, decomposition of limestone in cement industry.

117. Which natural process produces hydrocarbons?

a) Respiration

b) Marsh gas

c) Photosynthesis

d) Combustion

Explanation

The compounds composed of carbon and hydrogen only are called hydrocarbons. They are mainly produced naturally (marsh gas) and also by incomplete combustion of automobile fuel.

118. In which form earth surface radiates part of sun light energy to space?

a) Invisible light

b) Smoke

c) Longer wavelengths

d) Water vapor

Explanation

119. Assertion (A): The Greenhouse effect is a naturally occurring phenomenon.

Reasoning(R): Continuous emission of gases intensifies the greenhouses gases in the atmosphere.

a) Both A and R is True and R is the correct explanation of A.

b) Both A and R is True but R is not the correct explanation of A.

c) A is True but R is False.

d) Both A and R is False.

Explanation

Although the greenhouse effect is a naturally occurring phenomenon, it is intensified by the continuous emission of greenhouse gases into the atmosphere.

120. What are the impacts of increase in global temperature?

a) Melting of polar ice caps.

b) Flooding of low lying areas.

c) Increase of infectious diseases.

d) All the above

Explanation

During the past 100 years the amount of carbon dioxide in the atmosphere increased by roughly 30 percent and the amount of methane more than doubled. If these trends continue, the average global temperature will increase which can lead to melting of polar ice caps and flooding of low lying areas. This will increase incidence of infectious diseases like dengue, malaria.

121. Assertion (A): The pH of rain water drops below the level of 5.6 and results in acid rain.

Reasoning(R): Oxides of sulphur and nitrogen in the atmosphere are chemically converted into sulphuric and nitric acid.

a) Both A and R is True and R is the correct explanation of A.

b) Both A and R is True but R is not the correct explanation of A.

c) A is True but R is False.

d) Both A and R is False.

Explanation

122. Which of these produces the sulphur and nitrogen oxides?

a) Incomplete combustion of automobile fuels.

b) Petrol, diesel in motor engines.

c) Greenhouse effect

d) Marsh gas

Explanation

123. What are the negative impacts of acid rain?

a) Affects plants, animal life in aquatic ecosystem.

b) Dissolves and removes the nutrients needed for plants.

c) Respiratory ailments in humans and animals.

d) All the above

Explanation

Acid rain affects plants and animal life in aquatic ecosystem. It is harmful for agriculture, trees and plants as it dissolves and removes the nutrients needed for their growth. It corrodes water pipes resulting in the leaching of heavy metals such as iron, lead and copper into drinking water which has toxic effects. It causes respiratory ailment in humans and animals.

124. Which of these are composed of fine solid particles?

a) Smoke

b) Dust

c) Vapors

d) Fog

Explanation

Smoke particulate consists of solid particles (or) mixture of solid and liquid particles formed by combustion of organic matter. Condensation of vapors released during sublimation, distillation, boiling and calcination spray liquids and condensation of vapors. Dust composed of fine solid particles produced during crushing and grinding of solid materials.

125. Which measure of particles can enter the human lungs easily?

a) 10 micron

b) 50 micron

c) 5 micron

d) 0.1 micron

Explanation

Particulate pollutants bigger than 5 microns are likely to settle in the nasal passage whereas particles of about 10 micron enter the lungs easily and cause scaring or fibrosis of lung lining. They irritate the lungs and causes cancer and asthma. This disease is also called pneumoconiosis.

126. Who are all affected by the white lung disease?

a) Coal miners

b) Nuclear reactors

c) Textile workers

d) Pesticide producers

Explanation

Coal miners may suffer from black lung disease. Textile workers may suffer from white lung disease.

127. Which of the following statement is not correct regarding the effects of particulates?

a) Lead particulates affect children’s brain and interferes maturation of RCB.

b) Corrodes water pipes resulting in the leaching of heavy metals.

c) Particulates increase fog and rain in the clouds.

d) Particulates deposit on plants affect photosynthesis.

Explanation

Lead particulates affect children’s brain, interferes maturation of RBCs and even cause cancer. Particulates in the atmosphere reduce visibility by scattering and absorption of sunlight. It is dangerous for aircraft and motor vehicles. Particulates provide nuclei for cloud formation and increase fog and rain. Particulates deposit on plant leaves and hinder the intake of CO2 from the air and affect photosynthesis.

128. Which of the following is not found in the smog?

a) Non-volatile inorganic compounds

b) Oxides of nitrogen

c) Acidic aerosols

d) Ground level ozone

Explanation

Smog mainly consists of ground level ozone, oxides of nitrogen, volatile organic compounds, SO2, acidic aerosols and gases, and particulate matter.

129. Choose the correct statements about the photo chemical smog?

i) Photo chemical smog was first observed in the year 2000.

ii) Combination of smoke, dust and fog with air pollutants forms the photochemical fog.

iii) Photo chemical smog forms when the sun sets and becomes worse in the sun rise.

a) i only

b) ii only

c) iii only

d) None of the above

Explanation

130. In which region the loss of ozone molecules is known as depletion of stratospheric ozone?

a) Above Ionosphere

b) Upper atmosphere

c) Between Troposphere and surface of earth

d) Lower atmosphere

Explanation

The loss of ozone molecules in the upper atmosphere is termed as depletion of stratospheric ozone.

131. Which of this process converts the inert nitrous oxides in the stratosphere?

a) Electro chemical

b) Photo chemical

c) Thermocouple

d) Combustion

Explanation

Inert nitrous oxide in the stratosphere is photo chemically converted into more reactive nitric oxide. Oxides of nitrogen catalyze the decomposition of ozone and are themselves regenerated.

132. Choose the correct statements about CFC.

i) Supersonic aircrafts and jumbo jets exhaust CFC in the upper stratosphere.

ii) CFC passes from stratosphere to upper atmosphere.

iii) CFC stays only for a shorter period in the stratosphere.

a) i only

b) ii only

c) iii only

d) All the above

Explanation

CFC’s are the exhaust of supersonic air crafts and jumbo jets flying

in the upper atmosphere. They slowly pass from troposphere to stratosphere. They stay for very longer period of 50 -100 years.

133. Assertion (A): ‘Save water, Water will save you’ shows the importance of water.

Reasoning(R): Maintaining the quality of water is equally important to save water.

a) Both A and R is True and R is the correct explanation of A.

b) Both A and R is True but R is not the correct explanation of A.

c) A is True but R is False.

d) Both A and R is False.

Explanation

The slogan, Save Water, Water will save you’ tell us the importance of water. Such slogans tell us to save water. Apart from saving water, maintaining its quality is also equally important.

134. How many sources of water pollution are classified?

a) 5

b) 2

c) 4

d) 3

Explanation

The source of water pollution is classified as Point and Non-point source.

135. Which of the following decompose the organic wastes in water?

a)Fish

b) Aquatic Plants

c) Microorganisms

d) All the above

Explanation

Microorganisms present in water decompose this organic matter and consume dissolved oxygen in water.

136. Which of these processes is called as algae bloom?

a) Enhanced plant growth in water bodies.

b) High level of toxins in water bodies.

c) Increased growth rate of aquatic life.

d) Sudden color change of the water bodies.

Explanation

137. Choose the Incorrect statements.

i) Metals, toxic pesticides are poisonous to fish and other aquatic life.

ii) Detergents and oil floats can be easily removed from the water bodies and it is harmless.

iii) Acids from mine drainage and salts from various sources contaminate the water sources.

a) i only

b) ii only

c) iii only

d) All the above

Explanation

A whole variety of chemicals from industries, such as metals and solvents are poisonous to fish and other aquatic life. Some toxic pesticides can accumulate in fish and shell fish and poison the people who eat them. Detergents and oils float and spoil the water bodies.Acids from mine drainage and salts from various sources can also contaminate water sources.

138. Which of these human organs are affected by the lead poisoning in water?

a) Liver

b) Brain

c) Nervous system

d) All the above

Explanation

Lead poisoning in water can lead to the severe damage of kidneys, liver, brain etc. it also affects central nervous system.

139. Which of the following is an alternate for chlorinated hydrocarbon pesticides?

a) Sulphur

b) Neem

c) Animal wastes

d) All the above

Explanation

Neem based pesticides have been synthesized, which are safer than the chlorinated hydrocarbons. Every individual has an important role for preventing pollution and improving our environment

140. What is termed as the Global warming potential?

a) Heat retaining capacity of greenhouse gases.

b) Polluting factor of toxic gases.

c) Exceeding limit of toxins in the atmosphere.

d) Harmful chemical reactions in the atmosphere.

Explanation

Heat retaining capacity of greenhouse gases are called Global Warming Potential (GWP).

11th Science Lesson 8 Questions in English

8] Chemical Bonding

1. In which year the Linus Carl Pauling was awarded Nobel Prize for his research?

a) 1982

b) 1954

c) 1948

d) 1970

Explanation

Linus Carl Pauling was an American chemist, biochemist, peace activist, author and educator. In addition to his contribution to chemistry and he also worked with many biologists. He received the Nobel Prize in Chemistry in 1954 for his research into the nature of the chemical bond and its application to the elucidation of the structure of complex substances.

2. Choose the Incorrect statements.

i) Hydrogen and Oxygen are monoatomic and the inert gases are diatomic.

ii) Sodium combines with chlorine and forms sodium chloride that readily dissolves in water.

iii) Carbon combines with chlorine to form carbon tetrachloride that is insoluble in water.

a) i only

b) ii only

c) iii only

d) None of the above

Explanation

Diamond is very hard while its allotrope graphite is very soft. Gases like hydrogen and oxygen are diatomic while the inert gases are monoatomic. Carbon combines with chlorine to form carbon tetrachloride, which is a liquid and insoluble (immiscible) in water. Sodium combines with chlorine atom to form sodium chloride, a hard and brittle compound that readily dissolves in water.

3. Which of these attractive forces hold the atoms together in a chemical bond?

a) Electron forces

b) Static forces

c) Interatomic forces

d) Wander Walsh forces

Explanation

The interatomic attractive forces which hold the constituent atoms/ions together in a molecule are called chemical bonds.

4. Who provided the logical explanation for the chemical bonding?

a) Kossel and Lewis

b) Heitler and London

c) F. Hund and Robert. S. Mulliken

d) Linus Pauling

Explanation

A logical explanation for chemical bonding was provided by Kossel and Lewis in 1916.

5. Which of these facts is not true based on the Kossel and Lewis approach on chemical bonding?

a) The inertness of the noble gases is the basis for the chemical bonding.

b) Noble gas has little or no tendency to combine with other atoms.

c) Noble gases are not stable due to their completely filled outer shell electronic configuration.

d) Elements attain the completely filled configurations by losing, gaining or sharing on or more electrons.

Explanation

The Kossel and Lewis approach to chemical bonding is based on the inertness of the noble gases which have little or no tendency to combine with other atoms. They proposed that the noble gases are stable due to their completely filled outer shell electronic configuration. Elements other than noble gases, try to attain the completely filled electronic configurations by losing, gaining or sharing one or more electrons from their outer shell.

6. Which of these was introduced by G.N. Lewis?

a) Chemical bonding

b) Lewis dot structure

c) Diatomic nitrogen

d) Valence electrons

Explanation

G. N. Lewis proposed that the attainment of stable electronic configuration in molecules such as diatomic nitrogen, oxygen is achieved by mutual sharing of the electrons. He introduced a simple scheme to represent the chemical bond and the electrons present in the outer shell of an atom, called Lewis dot structure.

7. Which of the following is represented by the small dots in the Lewis dot scheme?

a) Valence electrons

b) Number of protons

c) Atomic number

d) Number of electrons

Explanation

In the Lewis dot scheme, the valence electrons (outer shell electrons) of an element are represented as small dots around the symbol of the element. The first four valence electrons are denoted as single dots around the four sides of the atomic symbol and then the fifth onwards, the electrons are denoted as pairs.

8. Which of these has two electrons in the valence shell?

a) Nitrogen

b) Oxygen

c) Hydrogen

d) Helium

Explanation

Only exception to this is helium which has only two electrons in its valence shell which is represented as a pair of dots (duet).

9. Which of the following is based on the Kossel-Lewis idea of chemical bonding?

a) Gravitational concept

b) Octet rule

c) Relativity theory

d) Electro static theory

Explanation

The idea of Kossel – Lewis approach to chemical bond lead to the octet rule which states that the atoms transfer or share electrons so that all atoms involved in chemical bonding obtain 8 electrons in their outer shell (valence shell)”.

10. Based on which of these the chemical bonds are classified?

a) Materials involved in the bonding.

b) Number of atoms present in the bonds.

c) Nature of interaction between the bonded atoms.

d) All the above

Explanation

The chemical bonds can be classified based on the nature of the interaction between the bonded atoms. Two major types of chemical bonds are covalent bonds and ionic bonds. Generally metals react with non-metals to form ionic compounds and the covalent bonds are present in the compounds formed by non-metals.

11. Define Covalent bond.

a) Mutual sharing of one or more pairs of electrons between two combining atoms.

b) Two atoms share just one pair of electron.

c) Metals reacting with non-metals to form covalent bonds.

d) External sharing of one electron between two atoms.

Explanation

In the case of oxygen molecule, both the oxygen atoms share two electron pairs between them and in nitrogen molecule three electron pairs are shared between two nitrogen atoms. This type of mutual sharing of one or more pairs of electrons between two combining atoms results in the formation of a chemical bond called a covalent bond.

12. Which of these molecules has a single covalent bond?

a) Helium molecule

b) Hydrogen molecule

c) Oxygen molecule

d) Nitrogen molecule

Explanation

If two atoms share just one pair of electron a single covalent bond is formed as in the case of hydrogen molecule. If two or three electron pairs are shared between the two combining atoms, then the covalent bond is called a double bond or a triple bond, respectively.

13. Which of these are denoted by pair of dots on the individual atoms in the Lewis structure?

a) Shared pair of valence electrons

b) Total number of shared electrons

c) Unshared electrons

d) Atomic value of individual atom

Explanation

Lewis structure (Lewis dot structure) is a pictorial representation of covalent bonding between the combining atoms. In this structure the shared valence electrons are represented as a pair of dots between the combining atoms and the unshared electrons of the atoms are represented as a pair of dots (lone pair) on the respective individual atoms.

14. What is the skeletal structure of the water?

a) O 2 H

b) H H O

c) H O H

d) 2 H O

Explanation

Draw the skeletal structure of the molecule. In general, the less electronegative atom is placed at the center. Hydrogen and fluorine atoms should be placed at the terminal positions. For water, the skeletal structure is

15. In which of these cases the number of negative charges is added to the number of valence electrons?

a) Anion

b) Polyatomic gas

c) Cation

d) Positive ions

Explanation

Calculate the total number of valence electrons of all the atoms in the molecule. In case of polyatomic ions the charge on ion should also be considered during the calculation of the total number of valence electrons. In case of anions the number of negative charges should be added to the number of valence electrons. For positive ions the total number of positive charges should be subtracted from the total number of valence electrons.

16. How many valence electrons will account for a single bond in the Lewis structure?

a) 1

b) 4

c) 2

d) 6

Explanation

Draw a single bond between the atoms in the skeletal structure of the molecule. Each bond will account for two valence electrons (a bond pair). For water, we can draw two bonds accounting for four valence electrons as follows.

17. Assertion (A): The Valence electrons are distributed after the bond formation as pairs by the octet rule.

Reasoning(R): Most electronegative atoms are distributed the lone pairs first then followed by other atoms.

a) Both A and R is True and R is the correct explanation of A.

b) Both A and R is True but R is not the correct explanation of A.

c) A is True but R is False.

d) Both A and R is False.

Explanation

Distribute the remaining valence electrons as pairs (lone pair), giving octet (only duet for hydrogen) to the atoms in the molecule. The distribution of lone pairs starts with the most electronegative atoms followed by other atoms.

18. What is used for satisfying the octet rule in the atoms?

a) Lone pairs

b) Valence electrons

c) Shared electrons

d) All the above

Explanation

Verify whether all the atoms satisfy the octet rule (for hydrogen duet). If not, use the lone pairs of electrons to form additional bond to satisfy the octet rule. In case of water, oxygen has octet and the hydrogen have duets, hence there is no need for shifting the lone pairs.

19. State the correct Lewis structure for Sulphur trioxide.

Explanation

The Lewis dot structures for some molecules

20. Which of the following is not a guideline for representing the Lewis structure?

a) A structure with all formal charges are zero is preferred over the one with charges.

b) A structure with small formal charges is preferred over the higher formal charges.

c) A structure with lone pairs are preferred than the duet pairs of atoms.

d) A structure in which negative formal charges are placed on the most electronegative atom is preferred.

Explanation

After calculating the formal charges, the best representation of Lewis structure can be selected by using following guidelines. A structure in which all formal charges are zero preferred over the one with charges. A structure with small formal charges is preferred over the one with higher formal charges. A structure in which negative formal charges are placed on the most electronegative atom is preferred.

21. Which of the following is not an exception for the octet rule categorization?

a) Molecules containing even electrons.

b) Molecules with electron deficient central atoms.

c) Molecules containing odd electrons.

d) Molecules with expanded valence shells.

Explanation

The octet rule is useful for writing Lewis structures for molecules with second period element as central atoms. In some molecules, the central atoms have less than eight electrons around them while some others have more than eight electrons. Exception to the octet rule can be categorized into following three types. Molecules with electron deficient central atoms, Molecules containing odd electrons and Molecules with expanded valence shells.

22. Which of the following have more than eight electrons around the central atom?

a) SF₃

b) PCl₂

c) PCl₅

d) SF₂

Explanation

In molecules such as sulphur hexafluoride (SF₆), phosphorous penta chloride (PCl₅) the central atom has more than eight valence electrons around them. Here the central atom can accommodate additional electron pairs by using outer vacant d orbitals. In SF6 the central atom sulphur is surrounded by six bonding pair of electrons or twelve electrons.

23. Choose the correct statements.

i) The combining atoms attain the nearest inert gas configuration when the electronegativity difference is small.

ii) The complete transfer of electrons between the atoms leads to the formation of a cation and an anion.

iii) The Anion and cation are held together by the electrostatic attractive force known as covalent bond.

a) i only

b) ii only

c) iii only

d) All the above

Explanation

When the electronegativity difference between the two combining atoms is large, the least electronegative atom completely transfers one or more of its valence electrons to the other combining atom so that both atoms can attain the nearest inert gas electronic configuration. The complete transfer of electron leads to the formation of a cation and an anion. Both these ions are held together by the electrostatic attractive force which is known as ionic bond.

24. In which of these bonds combining atoms donates a pair of electrons and share them commonly?

a) Special ionic bond

b) Shared ionic bond

c) Co-ordinate covalent bond

d) Combined covalent bond

Explanation

In certain bond formation, one of the combining atoms donates a pair of electrons i.e. two electrons which are necessary for the covalent bond formation and these electrons are shared by both the combining atoms. These types of bonds are called coordinate covalent bond or coordinate bond. The combining atom which donates the pair of electron is called a donor atom and the other atom an acceptor atom. This bond is denoted by an arrow starting from the donor atom pointing towards the acceptor atom.

25. What is defined as the bond length?

a) Distance between the valence bonds of combining atoms.

b) Distance between the nuclei of two covalent bond atoms.

c) Maximum distance between the nuclei and the valence bond.

d) Minimum distance shared between the covalent bond atoms.

Explanation

Bond length: The distance between the nuclei of the two covalently bonded atoms is called bond length. Consider a covalent molecule A-B. The bond length is given by the sum of the radii of the bonded atoms (rA + rB).

26. Which of the following are used to determine the bond length?

a) Spectroscopic Technique

b) X-ray diffraction Technique

c) Electron-diffraction Technique

d) All the above

Explanation

The length of a bond can be determined by spectroscopic, x-ray diffraction and electron-diffraction techniques.

27. Which of the following statement is not true regarding the bond length?

a) The size of the atom decides the length of the bond.

b) The number of valence electrons will decrease the bond length.

c) The number of bonds between the combining atoms also decides the bond length.

d) Greater the size of the atom the bond length will also be greater.

Explanation

The bond length depends on the size of the atom and the number of bonds (multiplicity) between the combining atoms. Greater the size of the atom greater will be the bond length. For example, carbon-carbon single bond length (1.54 Å) is longer than the carbon-nitrogen single bond length (1.43 Å).

28. Choose the correct statements.

i) Bond order is defined as the number of bonds formed between the two bonded atoms.

ii) The Bond order is equal to the number of shared pair of electrons between the two bonded atoms.

a) i only

b) ii only

c) Both i and ii

d) Neither i nor ii

Explanation

The number of bonds formed between the two bonded atoms in a molecule is called the bond order. In Lewis theory, the bond order is equal to the number of shared pair of electrons between the two bonded atoms. For example in hydrogen molecules, there is only one shared pair of electrons and hence, the bond order is one. Similarly in H2O, HCl, Methane, etc the central atom forms single bonds with bond order of one.

29. Assertion (A): The fixed angle between two covalent bonds in a molecule is defined as Bond angle.

Reasoning(R): The Covalent bonds are directional in nature and oriented in specific directions in space.

a) Both A and R is True and R is the correct explanation of A.

b) Both A and R is True but R is not the correct explanation of A.

c) A is True but R is False.

d) Both A and R is False.

Explanation

Covalent bonds are directional in nature and are oriented in specific directions in space. This directional nature creates a fixed angle between two covalent bonds in a molecule and this angle is termed as bond angle.

30. Which of the following statement is not correct regarding the bond angle?

a) The Spectroscopic methods are used to determine the bond angle.

b) Bond angle is expressed in degrees.

c) Bond angle is used to determine the size of the atom.

d) The bond angle can give idea about the shape of the molecule.

Explanation

Bond angle is usually expressed in degrees. The bond angle can be determined by spectroscopic methods and it can give some idea about the shape of the molecule.

31. Which of these atoms define the bond angle for CH4?

a) C only

b) C, H only

c) H, O only

d) H only

Explanation

Bond angles for some common molecules

32. In which state the bond enthalpy is defined for the molecules?

a) Solid state

b) Liquid state

c) Gaseous state

d) All the above

Explanation

The bond enthalpy is defined as the minimum amount of energy required to break one mole of a particular bond in molecules in their gaseous state.

33. What is the unit of bond enthalpy?

a) k mol

b) kJ mol^-1

c) kJ

d) J mol^-2

Explanation

The unit of bond enthalpy is kJ mol^-1.

34. Which of the below statements are not true about the bond enthalpy?

a) Larger the value of bond enthalpy stronger the bond.

b) The bond energy value depends on the size of the atoms.

c) The number of bonds between the bonded atoms decides the bond angles.

d) Larger the size of atoms involved lesser the bond enthalpy.

Explanation

Larger the bond enthalpy, stronger will be the bond. The bond energy value depends on the size of the atoms and the number of bonds between the bonded atoms. Larger the size of the atom involved in the bond, lesser is the bond enthalpy.

35. Identify the Incorrect Match.

BOND TYPE BOND LENGTH

A. C-C i) 1.54

B. H-Cl ii) 1.27

C. H-H iii) 1.33

D. C-I iv) 2.13

a) i only

b) ii only

c) iii only

d) iv only

Explanation

Bond lengths and bond enthalpies of some common bonds.

36. Assertion (A): Resonance structures differ in the position of bonding and lone pair of electrons.

Reasoning(R): Resonance phenomenon occurs at some molecules which has more than one valid Lewis structures.

a) Both A and R is True and R is the correct explanation of A.

b) Both A and R is True but R is not the correct explanation of A.

c) A is True but R is False.

d) Both A and R is False.

Explanation

Resonance: When we write Lewis structures for a molecule, more than one valid Lewis structures are possible in certain cases. For example let us consider the Lewis structure of carbonate ion [CO3]2-.The skeletal structure of carbonate ion (The oxygen atoms are denoted as OA, OB & OC relative position of the atoms are same. They only differ in the position of bonding and lone pair of electrons. Such structures are called resonance structures (canonical structures) and this phenomenon is called resonance.

37. Choose the incorrect statements.

i) All the carbon-oxygen bonds in carbonate ion are equivalent.

ii) The actual structure of the molecules is said to be the resonance hybrid an average of ten resonance forms.

iii) A single Lewis structure is not enough to picture the resonance hybrid.

a) i only

b) ii only

c) iii only

d) None of the above

Explanation

It is evident from the experimental results that all carbon-oxygen bonds in carbonate ion are equivalent. The actual structure of the molecules is said to be the resonance hybrid, an average of these three resonance forms. It is important to note that carbonate ion does not change from one structure to another and vice versa. It is not possible to picture the resonance hybrid by drawing a single Lewis structure.

38. Choose the correct statements.

i) The energy of the resonance hybrid structures is higher than that of all possible canonical structures.

ii) The Resonance energy is the energy difference between the most stable canonical structures and the resonance hybrid structures.

a) i only

b) ii only

c) Both i and ii

d) Neither i nor ii

Explanation

It is found that the energy of the resonance hybrid (structure 4) is lower than that of all possible canonical structures (Structure 1, 2 & 3). The difference in energy between most stable canonical structure and resonance hybrid is called resonance energy.

39. Assertion (A): In a covalent bond of two identical atoms both have equal tendency to attract the shared pair of electrons.

Reasoning(R): In a covalent bond of atoms having different electro negativities, the atom with higher electronegativity will have greater tendency to attract the shared pair of electrons.

a) Both A and R is True and R is the correct explanation of A.

b) Both A and R is True but R is not the correct explanation of A.

c) A is True but R is False.

d) Both A and R is False.

Explanation

When a covalent bond is formed between two identical atoms (as in the case of H2, O2, Cl2 etc…) both atoms have equal tendency to attract the shared pair of electrons and hence the shared pair of electrons lies exactly in the middle of the nuclei of two atoms. However, in the case of covalent bond formed between atoms having different electro negativities, the atom with higher electronegativity will have greater tendency to attract the shared pair of electrons more towards itself than the other atom. As a result the cloud of shared electron pair gets distorted.

40. Define Dipole.

a) Difference between the electro negativities of all the connected atoms.

b) Maximum value between the shared pair of electrons.

c) A small, equal and opposite charges are separated by a small distance.

d) All the above

Explanation

The electro negativities of hydrogen and fluorine on Pauling’s scale are 2.1 and 4 respectively. It means that fluorine attracts the shared pair of electrons approximately twice as much as the hydrogen which leads to partial negative charge on fluorine and partial positive charge on hydrogen. Hence, the H-F bond is said to be polar covalent bond. Here, a very small, equal and opposite charges are separated by a small distance (91pm) and is referred to as a dipole.

41. What is the value of the dipole moment?

a) μ = q × 2d

b) μ = q d

c) μ = q / 2d

d) μ = q + d

Explanation

The polarity of a covalent bond can be measured in terms of dipole moment which is defined as μ = q × 2d Where μ is the dipole moment, q is the charge and 2d is the distance between the two charges.

42. Choose the correct statements.

i) The Value of dipole moment of a covalent bond is a vector.

ii) The dipole moment vector points from the positive charge to negative charge.

a) i only

b) ii only

c) Both i and ii

d) Neither i nor ii

Explanation

The dipole moment is a vector and the direction of the dipole moment vector points from the negative charge to positive charge.

43. In which of these values the dipole moment is expressed?

a) Joule

b) Newton

c) Kilowatt

d) Debye

Explanation

The unit for dipole moment is columb meter (C m). It is usually expressed in Debye unit (D). The conversion factor is 1 Debye = 3.336 x 10^-30C m

44. Which of the following is not a polar molecule or a non-zero dipole moment?

a) HF

b) O₂

c) HCl

d) NO

Explanation

Diatomic molecules such as H₂, O₂, F₂ have zero dipole moment and are called non polar molecules and molecules such as HF, HCl, CO, NO have non zero dipole moments and are called polar molecules.

45. Assertion (A): Diatomic molecules have zero dipole moment and called as non-polar molecules.

Reasoning(R): All the polar bond molecules have a dipole moment value.

a) Both A and R is True and R is the correct explanation of A.

b) Both A and R is True but R is not the correct explanation of A.

c) A is True but R is False.

d) Both A and R is False.

Explanation

Molecules having polar bonds will not necessarily have a dipole moment. For example, the linear form of carbon dioxide has zero dipole moment, even though it has two polar bonds. In CO₂, the dipole moments of two polar bonds (CO) are equal in magnitude but have opposite direction. Hence, the net dipole moment of the CO₂ is, μ = μ1 + μ2 = μ1 + (-μ1) = 0

46. What is the dipole moment of the water?

a) 2.5D

b) 1 D

c) 1.85D

d) 11.5D

Explanation

Dipole moment in water is found to be 1.85D

47. Match the common molecules with its Dipole moment.

A. NH₃ i) 1.91

B. CHCl₃ii) 1.85

C. HF iii) 1.04

D. H₂O iv) 1.47

a) ii, iii, iv, i

b) iv, iii, i, ii

c) ii, iv, i, iii

d) i, iv, iii, ii

Explanation

Dipole moments of common molecules

48. What is used to predict the percentage of the ionic character of the atoms?

a) Electronegativity difference

b) Number of bonded pairs

c) Total number of shared electrons

d) Number of protons

Explanation

The extent of ionic character in a covalent bond can be related to the electro negativity difference to the bonded atoms.

49. What is the electronegativity difference value that decides the ionic character of the atoms?

a) 0.7

b) 11.7

c) 1.7

d) 111.7

Explanation

In a typical polar molecule the electronegativity difference can be used to predict the percentage of ionic character as follows. If the electronegativity difference is equal to 1.7, then the bond A-B has 50% ionic character if it is greater than 1.7, then the bond A-B has more than 50% ionic character, and if it is lesser than 1.7, then the bond A-B has less than 50% ionic character.

50. Which of these characters of the ionic compounds can be explained by the Polarization?

a) Partial covalent character

b) Bond enthalpy

c) Bond energy

d) Number of bonds

Explanation

Like the partial ionic character in covalent compounds, ionic compounds show partial covalent character. For example, the ionic compound, lithium chloride shows covalent character and is soluble in organic solvents such as ethanol. The partial covalent character in ionic compounds can be explained on the basis of a phenomenon called polarization.

51. Choose the incorrect statements about the mechanism the polarization.

i) In an ionic compound the negative charged cation attracts the valence electrons of cation while attracting the nucleus.

ii) The distortion in the electron cloud of the anion drifts the density towards cation and shares the valence electrons.

a) i only

b) ii only

c) Both i and ii

d) Neither i nor ii

Explanation

We know that in an ionic compound, there is an electrostatic attractive force between the cation and anion. The positively charged cation attracts the valence electrons of anion while repelling the nucleus. This causes a distortion in the electron cloud of the anion and its electron density drifts towards the cation, which results in some sharing of the valence electrons between these ions. Thus, a partial covalent character is developed between them. This phenomenon is called polarization.

52. Which is known as the polarisibility?

a) Total number of non-polarized atoms

b) Tendency of an anion to get polarized

c) Extent of polarization

d) Number of atoms polarized

Explanation

The ability of a cation to polarize an anion is called its polarizing ability and the tendency of an anion to get polarized is called its polarisibility. The extent of polarization in an ionic compound is given by the Fajans rules

53. Assertion (A): The Increase in charge on cation or in anion will increase the covalent character.

Reasoning(R): The Polarisibility is increased if the magnitude of negative charge on the anion is higher.

a) Both A and R is True and R is the correct explanation of A.

b) Both A and R is True but R is not the correct explanation of A.

c) A is True but R is False.

d) Both A and R is False.

Explanation

Fajans Rules: To show greater covalent character, both the cation and anion should have high charge on them. Higher the positive charge on the cation, greater will be the attraction on the electron cloud of the anion. Similarly higher the magnitude of negative charge on the anion, greater is its polarisibility. Hence, the increase in charge on cation or in anion increases the covalent character.

54. Which of these shows greater covalent character due to greater extent of polarization?

a) Smaller cation and larger anion

b) Equal cation and anion

c) Larger cation and smaller anion

d) Varying anion and cation

Explanation

The smaller cation and larger anion show greater covalent character due to the greater extent of polarization.

55. Which of these will be useful in predicting the shape of molecules?

a) Lewis theory alone

b) Number of combining atoms

c) Lewis theory with VSEPR theory

d) Number of cations and anion

Explanation

Lewis concept of structure of molecules deals with the relative position of atoms in the molecules and sharing of electron pairs between them. However, we cannot predict the shape of the molecule using Lewis concept. Lewis theory in combination with VSEPR theory will be useful in predicting the shape of molecules.

56. Which of these will depend on the number of valence shell electron pair of the molecules according to VSEPR theory?

a) Number of Lone pairs

b) Shape of molecules

c) Total number of bonded pairs

d) Number of valence electron

Explanation

Important principles of VSEPR Theory are as follows: The shape of the molecules depends on the number of valence shell electron pair around the central atom.

57. Choose the correct statements.

i) Various numbers of electron pairs are available in that bond pairs and lone pairs are one of them.

ii) Lone pairs are the valence electron pairs which are not involved in bonding.

a) i only

b) ii only

c) Both i and ii

d) Neither i nor ii

Explanation

There are two types of electron pairs namely bond pairs and lone pairs. The bond pair of electrons are those shared between two atoms, while the lone pairs are the valence electron pairs that are not involved in bonding.

58. Which of this order denotes the repulsive interaction between the types of electron pairs as per VSEPR theory?

a) lp – lp > lp – bp > bp- bp

b) lp – lp < lp – bp < bp-bp

c) lp – lp > bp – bp > lp-bp

d) lp – lp < lp – bp > bp-bp

Explanation

Each pair of valence electrons around the central atom repels each other and hence, they are located as far away as possible in three dimensional spaces to minimize the repulsion between them. The repulsive interaction between the different types of electron pairs is in the following order. lp – lp > lp – bp > bp-bp where lp- lone pair; bp- bond pair.

59. Why the lone pairs have greater repulsive power in a molecule?

a) Lone pairs are localized on the central atom.

b) Lone pairs interact with only one nucleus.

c) Lone pairs occupy more space than bond pairs.

d) All the above

Explanation

The lone pair of electrons are localized only on the central atom and interacts with only one nucleus whereas the bond pairs are shared between two atoms and they interact with two nuclei. Because of this the lone pairs occupy more space and have greater repulsive power than the bond pairs in a molecule.

60. Which of the following has a v- shape or bent shape geometry?

a) CO₂

b) HCN

c) O₃

d) BF₃

61. Identify the incorrect Match

A. Trigonal planar i) HCHO

B. Tetrahedral ii) CS₂

C. Linear iii) BeCl₂

D. Bent shape iv) PbCl₂

a) i only

b) ii only

c) iii only

d) iv only

Explanation

Shapes of molecules predicted by VSEPR theory.

62. Which of these molecules has single lone pair?

a) AB₂L₂

b) AB₃L

c) AB₅

d) AB₃L₂

Explanation

63. Which of this molecule does not have a square pyramidal geometry?

a) BrF₅

b) XeOF₄

c) XeF₄

d) TeF^–₅

64. What is the molecular geometry shape of the molecule AB₇?

a) Pentagonal bi-pyramidal

b) Linear

c) Square planar

d) Octahedral

Explanation

65. Who gave the theoretical explanation for the covalent bond in hydrogen?

a) Linus Carl Pauling

b) Kossel and Lewis

c) Heitler and London

d) Pauling and Slater

Explanation

Heitler and London gave a theoretical treatment to explain the formation of covalent bond in hydrogen molecule on the basis of wave mechanics of electrons. It was further developed by Pauling and Slater.

66. Which of this statement is not a salient feature of VB theory?

a) Greater the overlap slows down the energy and the weakest bond is formed.

b) A covalent bond will be formed when half-filled orbitals of two atoms overlap.

c) Orbital overlap takes place in the direction that maximizes the overlap.

d) The strength of a covalent bond depends upon the extent of overlap of atomic orbitals.

Explanation

Salient features of VB Theory: When half-filled orbitals of two atoms overlap, a covalent bond will be formed between them. The resultant overlapping orbital is occupied by the two electrons with opposite spins. For example, when H2 is formed, the two 1s electrons of two hydrogen atoms get paired up and occupy the overlapped orbital. The strength of a covalent bond depends upon the extent of overlap of atomic orbitals. Greater the overlap, larger is the energy released and stronger will be the bond formed. Each atomic orbital has a specific direction (except s-orbital which is spherical) and hence orbital overlap takes place in the direction that maximizes overlap

67. By which of these the covalent bond is classified as sigma and pi bonds?

a) Extent of polarization

b) Nature of overlap

c) Direction of overlap

d) Strength of overlap

Explanation

When atoms combine to form a covalent molecule, the atomic orbitals of the combining atoms overlap to form a covalent bond. The bond pair of electrons will occupy the overlapped region of the orbitals. Depending upon the nature of overlap we can classify the covalent bonding between the two atoms as sigma (σ) and pi (π) bonds.

68. Which of these bonds are created by two atomic orbitals overlapping linearly along the axis?

a) Sigma bond

b) Head-on overlap

c) Axial overlap

d) All the above

Explanation

Sigma and Pi bonds: When two atomic orbitals overlap linearly along the axis, the resultant bond is called a sigma (σ) bond. This overlap is also called ‘head-on overlap’ or ‘axial overlap’.

69. Assertion (A): Overlap of s orbital and two p orbitals along the molecular axis results in sigma bond formation.

Reasoning(R): If the x-axis is considered as molecular axis the overlap will result in sigma bond.

a) Both A and R is True and R is the correct explanation of A.

b) Both A and R is True but R is not the correct explanation of A.

c) A is True but R is False.

d) Both A and R is False.

Explanation

Overlap involves an s orbital (s-s and s-p overlaps) will always result in a sigma bond as the s orbital is spherical. Overlap between two p orbitals along the molecular axis will also result in sigma bond formation. When we consider x-axis as molecular axis, the p_x–p_x overlap will result in σ-bond.

70. In which ways the two atomic orbitals overlap to form a pi bond?

a) Sideways

b) Perpendicular

c) Linearly

d) Parallel

Explanation

When two atomic orbitals overlap sideways, the resultant covalent bond is called a pi (π) bond. When we consider x-axis as molecular axis, the p_y– p_y and p_z– p_z overlaps will result in the formation of a π-bond.

71. Which of this molecule has a s-s overlap and a sigma covalent bond?

a) Helium

b) Hydrogen

c) Ozone

d) Hydrogen Sulphide

Explanation

Formation of hydrogen (H₂) Molecule: Electronic configuration of hydrogen atom is 1s1 during the formation of H₂ molecule, the 1s orbitals of two hydrogen atoms containing one unpaired electron with opposite spin overlap with each other along the inter-nuclear axis. This overlap is called s-s overlap. Such axial overlap results in the formation of a σ-covalent bond.

72. In which axis the sigma covalent bond is formed in a fluorine molecule?

a) x- axis

b) z- axis

c) y- axis

d) All the above

Explanation

Formation of fluorine molecule (F2): Valence shell electronic configuration of fluorine atom: 2s2 2px 2, 2py 2, 2pz 1. When the half-filled pz orbitals of two fluorine overlap along the z-axis, a σ-covalent bond is formed between them.

73. Assertion (A): Bonding in simple and complex molecules can be explained on the basis of overlap of the combining atoms.

Reasoning(R): The Polyatomic molecules cannot be explained on the basis of simple overlap of atomic orbitals.

a) Both A and R is True and R is the correct explanation of A.

b) Both A and R is True but R is not the correct explanation of A.

c) A is False but R is True.

d) Both A and R is False.

Explanation

Bonding in simple molecules such as hydrogen and fluorine can easily be explained on the basis of overlap of the respective atomic orbitals of the combining atoms. But the observed properties of polyatomic molecules such as methane, ammonia, beryllium chloride etc. cannot be explained on the basis of simple overlap of atomic orbitals. For example, it was experimentally proved that methane has a tetrahedral structure and the four C-H bonds are equivalent. This fact cannot be explained on the basis of overlap of atomic orbitals of hydrogen (1s) and the atomic orbitals of carbon with different energies (2s2 2px 2 2py 2pz).

74. Who introduced the concept of hybridization of atomic orbitals?

a) Linus Pauling

b) Lewis

c) Kossel

d) Robert Mulliken

Explanation

Linus Pauling proposed that the valence atomic orbitals in the molecules are different from those in isolated atom and he introduced the concept of hybridization.

75. Which of these denotes the hybridization or the hybridized orbitals?

a) Process of mixing atomic orbitals of same atom to form equal number of new orbitals with same energy.

b) Process of mixing various orbital atoms to form new orbitals with higher energy.

c) Process of mixing same orbital atoms to form unequal number of atoms.

d) Process of mixing various orbital atoms to create lower energy atoms of equal number.

Explanation

Hybridization is the process of mixing of atomic orbitals of the same atom with comparable energy to form equal number of new equivalent orbitals with same energy. The resultant orbitals are called hybridized orbitals and they possess maximum symmetry and definite orientation in space so as to minimize the force of repulsion between their electrons.

76. Which of these concepts of bonding is not explained by the Lewis concept and Valence bond theory?

a) Chemical bonding

b) Nature of paramagnetic molecules

c) Molecular structure

d) Electron pair bond formation

Explanation

Lewis concept and valence bond theory qualitatively explains the chemical bonding and molecular structure. Both approaches are inadequate to describe some of the observed properties of molecules. For example, these theories predict that oxygen is diamagnetic. However, it was observed that oxygen in liquid form was attracted towards the poles of strong magnet, indicating that oxygen is paramagnetic. As both these theories treated the bond formation in terms of electron pairs and hence they fail to explain the bonding nature of paramagnetic molecules.

77. Who explained the magnetic behavior of the molecules?

a) Heitler and London

b) Linus Carl Pauling

c) F. Hund and Robert Mulliken

d) G.N. Lewis

Explanation

F. Hund and Robert. S. Mulliken developed a bonding theory called molecular orbital theory which explains the magnetic behavior of molecules.

78. Assertion (A): The shape of the molecular orbitals does not depend upon the shapes of combining atomic orbitals.

Reasoning(R): The identity of the individual atomic orbitals is not changed while combining to form new orbitals.

a) Both A and R is True and R is the correct explanation of A.

b) Both A and R is True but R is not the correct explanation of A.

c) A is True but R is False.

d) Both A and R is False.

Explanation

The salient features of Molecular orbital Theory (MOT): When atoms combine to form molecules, their individual atomic orbitals lose their identity and forms new orbitals called molecular orbitals. The shapes of molecular orbitals depend upon the shapes of combining atomic orbitals.

79. Choose the correct statements.

i) The number of molecular orbitals formed and the number of combining atomic orbitals are not same.

ii) Half the number of formed molecular orbitals has lower energy and half of them will have high energy.

iii) The anti-bonding molecular orbitals have low energy and the bonding material is of high energy.

a) i only

b) ii only

c) iii only

d) None of the above

Explanation

The number of molecular orbitals formed is the same as the number of combining atomic orbitals. Half the number of molecular orbitals formed will have lower energy than the corresponding atomic orbital, while the remaining molecular orbitals will have higher energy. The molecular orbital with lower energy is called bonding molecular orbital and the one with higher energy is called anti-bonding molecular orbital. The bonding molecular orbitals are represented as σ (Sigma), π (pi), δ (delta) and the corresponding anti-bonding orbitals are denoted as σ*, π* and δ*.

80. Which of these principles are followed for filling of electrons in the molecular orbitals?

a) Pauli’s exception principle

b) Hund’s rule

c) Aufbau’s principle

d) All the above

Explanation

The electrons in a molecule are accommodated in the newly formed molecular orbitals. The filling of electrons in these orbitals follows Aufbau’s principle, Pauli’s exclusion principle and Hund’s rule as in the case of filling of electrons in atomic orbitals.

81. Which of these is inferred by the bond order value of a molecule?

a) Number of covalent bonds between the combining atoms.

b) Total number of electrons present in anti-bonding molecular orbitals.

c) Total number of covalent and ionic bonds of a molecule.

d) Number of linear combinations in a molecule.

Explanation

Bond order gives the number of covalent bonds between the two combining atoms. The bond order of a molecule can be calculated using the following equation,

Where, N_b = Total number of electrons present in the bonding molecular orbitals and N_a = Total number of electrons present in the anti-bonding molecular orbitals

82. What is the value of bond order for a molecule that doesn’t exist?

a) Unity

b) Zero

c) Infinity

d) Fractional value

Explanation

A bond order of zero value indicates that the molecule doesn’t exist.

83. Which is the most common method for calculating the wave functions of the molecular orbits?

a) Schrodinger equation

b) Electroscopic methods

c) X-ray diffraction

d) Linear combination of atomic orbitals

Explanation

The wave functions for the molecular orbitals can be obtained by solving Schrödinger wave equation for the molecule. Since solving the Schrödinger equation is too complex, approximation methods are used to obtain the wave function for molecular orbitals. The most common method is the linear combination of atomic orbitals (LCAO).

84. What is the anti-bonding molecular orbit value for the wave functions ψA and ψB?

a) ψA + ψB

b) ψA – ψB

c) ψA * ψB

d) ψA / ψB

Explanation

The atomic orbitals are represented by the wave function Ψ. Let us consider two atomic orbitals represented by the wave function ψA and ψB with comparable energy, combines to form two molecular orbitals. One is bonding molecular orbital (ψ bonding) and the other is anti-bonding molecular orbital (ψ anti-bonding). The wave functions for these two molecular orbitals can be obtained by the linear combination of the atomic orbitals ψA and ψB as below.

Ψ bonding = ψA + ψB ψ anti-bonding = ψA – ψB

The formation of bonding molecular orbital can be considered as the result of constructive interference of the atomic orbitals and the formation of anti-bonding molecular orbital can be the result of the destructive interference of the atomic orbitals.

85. Choose the Incorrect statements about the properties of metals.

i) The Metallic bond keeps the atoms of the metal so closely in a metallic crystal.

ii) The ionic bonds are formed between the atoms of different electro negativities.

iii) The Metallic bond is a covalent bond as the metals have sufficient number of valence electrons for mutual sharing.

a) i only

b) ii only

c) iii only

d) None of the above

Explanation

Metals have some special properties of lustre, high density, high electrical and thermal conductivity, malleability and ductility, and high melting and boiling points. The forces that keep the atoms of the metal so closely in a metallic crystal constitute what is generally known as the metallic bond. The metallic bond is not just an electrovalent bond (ionic bond), as the latter is formed between atoms of different electro negativities. Similarly, the metallic bond is not a covalent bond as the metal atoms do not have sufficient number of valence electrons for mutual sharing with 8 or 12 neighboring metal atoms in a crystal.

86. Which of these forces between in the metal ions makes closely packed crystals?

a) Ion repulsion

b) Electrostatic attraction

c) Magnetic deflection

d) Thermal equilibrium

Explanation

The electrostatic attraction between the metal ions and the free electrons yields a three-dimensional close packed crystal with a large number of nearest metal ions. So, metals have high density. As the close packed structure contains many slip planes along which movement can occur during mechanical loading, the metal acquires ductility.

87. Why the metallic bonding has no directional properties?

a) Each metal ion is surrounded by electron cloud in all directions.

b) The electron clouds reflect the light.

c) Metals are closely packed crystals with large number of ions.

d) Electrons are free to move around the positive ions.

Explanation

As each metal ion is surrounded by electron cloud in all directions, the metallic bonding has no directional properties.

88. Which of the following is not a quality of metals?

a) High electrical conductivity

b) Metallic luster

c) Low boiling point and low thermal conductivity

d) High melting points

Explanation

As the electrons are free to move around the positive ions, the metals exhibit high electrical and thermal conductivity. The metallic luster is due to reflection of light by the electron cloud. As the metallic bond is strong enough, the metal atoms are reluctant to break apart into a liquid or gas, so the metals have high melting and boiling points.

89. Assertion (A): The atoms in a crystal overlap to form numerous bonding and anti-bonding molecular orbitals without any gap.

Reasoning(R): The bonding orbitals are completely filled with an electron pair and the anti-bonding molecules are empty.

a) Both A and R is True and R is the correct explanation of A.

b) Both A and R is True but R is not the correct explanation of A.

c) A is True but R is False.

d) Both A and R is False.

Explanation

The bonding in metal is better treated by Molecular orbital theory. As per this theory, the atomic orbitals of large number of atoms in a crystal overlap to form numerous bonding and anti-bonding molecular orbitals without any band gap. The bonding molecular orbitals are completely filled with an electron pair in each, and the anti-bonding molecular orbitals are empty.

90. Choose the correct statements.

i) Absence of band gap accounts for the low electrical conductivity of metals.

ii) High thermal conductivity in metals is due to thermal excitation of many electrons from valence to conductance band.

iii) The temperature increase in metals increases the electrical conductivity due to vigorous thermal motion of lattice ions.

a) i only

b) ii only

c) iii only

d) All the above

Explanation

Absence of band gap accounts for high electrical conductivity of metals. High thermal conductivity is due to thermal excitation of many electrons from the valence band to the conductance band. With an increase in temperature, the electrical conductivity decreases due to vigorous thermal motion of lattice ions that disrupts the uniform lattice structure, that is required for free motion of electrons within the crystal.

91. Assertion (A): Most of the metals absorb light of all wavelengths and black in color.

Reasoning(R): Absorption of light of all wavelengths is due to absence of band gap in metals.

a) Both A and R is True and R is the correct explanation of A.

b) Both A and R is True but R is not the correct explanation of A.

c) A is True but R is False.

d) Both A and R is False.

Explanation

Most metals are black except copper, silver and gold. It is due to absorption of light of all wavelengths. Absorption of light of all wavelengths is due to absence of band gap in metals.

92. If a molecule has no unpaired electrons hence it is ______.

a) Paramagnetic

b) Diamagnetic

c) Both a and b

d) None of the above

Explanation

Molecule has two unpaired electrons. Hence it is paramagnetic. Molecule has no unpaired electrons. Hence it is diamagnetic.

September 15, 2022

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