Can I answer in Tamil at the time of interview in TNPSC?

Can I answer in Tamil at the time of interview in TNPSC?

It is definitely yes. You can answer to the questions bilingually i.e. in both English and Tamil. You should answer to the interview panel board by the way they can understand easily.

You should answer to the questions with utmost confidence. It is not about the language you answer ,it truly depends on how you answer the question.