The year 1921 is referred to as the ‘year of the demographic divide’ in India. This term is used because, after the 1921 census, India’s population growth rate started to show a marked shift. Prior to 1921, the population had been growing at a steady rate, but after this year, the population growth rate slowed down significantly. The reasons for this demographic divide are complex, involving factors such as famine, disease, and other socio-economic conditions that affected mortality rates.
Thus, the correct answer is (3) 1921.