Density of population tells us about :

The correct answer is Option (3) → number of individuals present per unit space in a given time

Option (1) total number of individuals of a species — Incorrect. This is the population size; density relates the number to the space.

Option (2) total area occupied by a species — Incorrect. This is the range of the species, not its density.

Option (3) number of individuals present per unit space in a given time — Correct. Population density (N) is the number per unit area or volume at a given time. It rises with births and immigration and falls with deaths and emigration.

Option (4) population growth in a particular time span — Incorrect. This is the growth rate, dN/dt. Growth is the change in density over a period, caused by natality, mortality, immigration and emigration. Density tells the number at one given time, not how much it changes.