Phenomenal and rapid increase of population in a short period is called

$Statement \; 1$: Zero population growth should be achieved as early as possible to control human population.
$Statement \; 2$: This requires not two children per couple but a little more effort on reduction of this number.

Assertion: The sex ratio of Kerala is the highest in India.
Reason: In countries like India,the population is increasing at a rapid rate.

Generally,there was a population growth rate increase in India,but in which of the following years was there a decrease in the population growth rate?

The population growth of India from $1981$ to $1991$ is (in $\%$)

Human population in India reached the $1$ billion mark by the year . . . . . . .