The annual growth rate percentage population in India gradually started declining in the year ______.

Correct option is B

1981
 Since 1981, growth rate of population in India has started declining gradually. This is because birth rate is declining as the people are becoming aware of advantages of small nuclear families over large families.
 Government has taken a number of measures and introduced family planning measures.
 The population of India recorded a negative growth rate in 1911-1921. The year 1921 is known as the year demographic divide because it is the only census year when there was a decrease in the growth of population.