The correct answer is b) 10 years.
The Census of India is a decennial (every 10 years) exercise conducted by the Office of the Registrar General and Census Commissioner, India. It is the largest civil registration exercise in the world. The first census was conducted in 1872. The last census was conducted in 2011. The next census will be conducted in 2021.
The census is used to collect data on the population of India, including age, sex, religion, language, literacy, and occupation. The data is used to plan for development and to monitor the progress of development.
The census is also used to collect data on households, including the number of members in the household, the type of housing, and the ownership of assets. The data is used to plan for housing and infrastructure development.
The census is a major undertaking that requires the cooperation of millions of people. It is a valuable source of information on the population of India and is used to plan for the future of the country.
The other options are incorrect because the census is not conducted every 5 years, 15 years, or 20 years.