According to the $1991$ census,the population density of Madhya Pradesh is:

$A$ biologist studied a rat population at the time of birth. He observed that the estimated births were $250$, estimated deaths were $240$, $20$ rats immigrated into the population, and $30$ rats emigrated from the population. What was the net increase in the population?

Define 'zero population growth rate'. Draw an age pyramid for the same.

In the given diagram,identify $a, b, c,$ and $d$. Specifically,identify $b$ and $c$.

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

Which one of the following population attributes contributes to an increase in population density?