Population density means

Members of a population:

If there were $30$ lotus plants in a pond last year and through reproduction $10$ new plants were added, taking the current population to $40$, then the birth rate = $.........$ offspring per lotus per year.

If natality is represented by $B$,mortality by $D$,immigration by $I$,emigration by $E$,and population density by $N$,then the population density at time $t+1$ is represented by:

In a village,the human population is $2000$. If the number of females is $1100$,what will be the sex ratio of the population?

Which of the following is not an attribute of a population?