The first census in India took place in 1872 . It was conducted by the British colonial administration to gather demographic data and administer their rule more effectively. The census aimed to collect information on population size, religion, caste, occupation, and socio-economic factors. It has since been conducted regularly every ten years and has played a crucial role in monitoring population growth and informing developmental plans and policies in India.

The year 1921 is referred to as the 'Demographic divide 'in India because it marked a significant shift in population trends and demographics in the country. 1921 census shows negative growth rate due to increase in death rate because of influenza epidemic of 1918 - 19.

The decades 1951-1981 are referred to as the period of population explosion in India, which was caused by a rapidfall in the mortality rate but a high fertility rate of population in the country.

Kerala has the highest sex ratio of 1084 in all Indian states. Puducherry has the second-highest sex ratio of 1038 in Indian states.

Haryana has the lowest sex ratio (877) in Indian states while in union territory Daman Diu has lowest sex ratio of 618.

15 - 64 range is usaually known as WAP  (Working Age Population) that allows demographic dividend.
The demographic dividend refers to a period when the working-age population (15-64 years) is larger in proportion to the dependent population (children and elderly), creating a favorable demographic structure for economic growth and development. During this stage, a country can potentially harness the economic benefits of a youthful and productive workforce.

All above factors combined forms  the features of Indian demography.

Malthus 'most famous work was his Essay on the Principle of Population, first published in 1798 and enlarged in later editions. This work contained his famous argument that human populations tend to grow faster than agricultural output, resulting in famines or crises.

In his 1798 work, An Essay on the Principle of Population, Malthus examined the relationship between population growth and resources. From this, he developed the Malthusian theory of population growth in which he wrote that population growth occurs exponentially in geometric progression, so it increases according to birth rate.

Positive checks on population growth refer to factors that naturally regulate population growth by increasing mortality rates or decreasing fertility rates. Warfares, famines, earthquakes, floods, diseases etc are all examples of positive checks.