Hint: The Census of India is held every decade. This has been started since 1871. In series of censuses, the 2001 Census of India was the 14th.
The results of this census were: the population of India was 1,028,737,436 which consist of 496,514,346 females and 532,223,090 males. When it comes to the religion demographics, $80.45\% $ were Hindus ($82.75$ crore), Muslims were $13.4\% $ ($13.8$ crore), Christians were $2\% $ , Sikh were $1.89\% $, Buddhist were $0.74\% $, Jain were $0.46\% $, Animist and the rest were the people of other religions of about $0.43\% $. Hindi is the language that is most widely spoken in the Northern parts of India. $53.6\% $ of the Indian population knows Hindi according to the 2001 census. Out of those, $41\% $ of them declared Hindi as their official language or mother tongue. English was known by $12.5\% $ of Indians according to the census 2001. The number of bilingual speakers in India was $25.50$ crore, which was $24.8\% $ of the total population of the 2001 census. Papua New Guinea is a country with the highest number of languages i.e., 839. India is in second place with 780 languages. According to the 2001 census, a literate person is one who is 7 years old and can read and write any language with understanding.
Thus, option (C) is correct.
Note: Census is the official count or the survey, especially of a population. In the 2001 census, around 700,000 people did not state their religion. Compared to the 1991 census, the population was increased by $21.5\% $ i.e., 182,310,397.