In a pond, there were $20$ lotus plants and $10$ new plants were added. Calculate the birth rate for the year.

Mortality is the rate of . . . . . . of individuals in a population.

$A$ biologist studied the population of rats in a barn. He found that the average natality was $250$, average mortality $240$, immigration $20$ and emigration $30$. The net increase in population is

The population of any species is:

Geometric representation of age structure is a characteristic of

The most important factor which determined the increase in human population in India during the $20^{\text{th}}$ century.