Which of the following Organisation calculate GDP in India?

Explanation: 

The Central Statistical Organisation (CSO) is the government agency responsible for calculating and publishing the Gross Domestic Product (GDP) in India. It compiles the national accounts data and provides the official GDP figures, which are used to assess the country's economic performance. The CSO operates under the Ministry of Statistics and Programme Implementation.

The correct answer is: a) C.S.O (Central Statistical Organisation)