Answer: (Detailed Solution Below)
Option A: 1921
Detailed Solution:
The correct answer is “1921”.
1921 is known as the "year of the great divide" because it marked a significant demographic turning point in India. Before 1921, India's population growth was relatively slow and inconsistent, largely due to high mortality rates caused by famines, epidemics, and poor health conditions. After 1921, the population began to grow steadily due to improvements in healthcare, reduction in famines, and overall better living conditions, marking a clear demographic shift.