With 1,210,193,422 residents reported in the 2011 provisional Census, India is the world's second-most populous country. Its population grew at 1.76% per annum during 2001–2011, down from 2.13% per annum in the previous decade (1991–2001).[ The human sex ratio, according to the 2011 census, is 940 females per 1,000 males. The median age was 24.9 in the 2001 census. Medical advances made in the last 50 years as well as increased agricultural productivity brought about by the "Green Revolution" have caused India's population to grow rapidly. India continues to face several public health-related challenges. According to the World Health Organisation, 900,000 Indians die each year from drinking contaminated water or breathing polluted air. There are around 50 physicians per 100,000 Indians. The number of Indians living in urban areas has grown by 31.2% between 1991 and 2001. Yet, in 2001, over 70% lived in rural areas. According to the 2001 census, there are 27 million-plus cities in India, with Mumbai, Delhi, Kolkata, and Chennai being the largest. The literacy rate in 2011 was 74.04%: 65.46% among females and 82.14% among males. Kerala is the most literate state; Bihar the least.
India is home to two major language families: Indo-Aryan (spoken by about 74% of the population) and Dravidian (24%). Other languages spoken in India come from the Austro-Asiatic and Tibeto-Burman language families. India has no national language. Hindi, with the largest number of speakers, is the official language of the government. English is used extensively in business and administration and has the status of a "subsidiary official language"; it is important in education, especially as a medium of higher education. Each state and union territory has one or more official languages, and the constitution recognises in particular 21 "scheduled languages". The Indian Constitution recognises 212 scheduled tribal groups which together constitute about 7.5% of the country's population. The 2001 census reported that Hinduism, with over 800 million adherents (80.5% of the population), was the largest religion in India; they are followed by Muslims (13.4%), Christians (2.3%), Sikhs (1.9%), Buddhists (0.8%), Jains (0.4%), Jews, Zoroastrians, and Bahá'ís. India has the world's largest Hindu, Sikh, Jain, Zoroastrian, and Bahá'í populations, and has the third-largest Muslim population and the largest Muslim population for a non-Muslim majority country.