Detailed Solution:
The correct answer is “1921”.
The year 1921 is known as the "Year of the Great Divide" in India's demographic history because it was the last year when India's population declined due to famine.
Before 1921, India's population was either not growing or growing very slowly due to famines, cholera, and plague epidemics. After 1921, India's population growth has been consistent and rapid.