The correct option is 1921-1951.
Explanation
India's demographic history is conventionally divided into four distinct phases based on the trends in population growth rates.
- Phase I (1901-1921): This period is referred to as the period of stagnant or stationary phase. The growth rate was very low, and the decade 1911-1921 even recorded a negative growth rate. Both birth rates and death rates were high due to poor health and medical services, widespread illiteracy, and inefficient distribution of food.
- Phase II (1921-1951): This period is characterised as the period of steady population growth. An overall improvement in health and sanitation throughout the country brought down the mortality rate. At the same time, better transport and communication systems improved distribution networks. The crude birth rate remained high, leading to a steady increase in population.
- Phase III (1951-1981): This period is known as the period of population explosion. It was caused by a rapid fall in the mortality rate but a high fertility rate of the population. Developmental activities and improved medical facilities contributed to this trend.
- Phase IV (Post-1981): This period is characterised by a high growth rate which has started slowing down. A downward trend in the crude birth rate is responsible for this deceleration.
Key Takeaway: The year 1921 is historically significant and is termed the 'Year of Great Divide' because it marks the transition from a fluctuating or stagnant population phase to a phase of continuous and steady growth.