Population density is the number of people per unit area. It is usually expressed as the number of people per square kilometer (km2) or square mile (mi2). Population density can be used to compare the population of different countries or regions, or to track changes in population over time.
The percentage of literate population is the proportion of the population that can read and write. It is usually expressed as a percentage. The percentage of literate population can be used to measure the level of education in a country or region.
The distribution of population across age groups is the way in which the population is divided into different age groups. It is usually expressed as a percentage of the total population. The distribution of population across age groups can be used to track changes in the age structure of a population, and to identify potential problems such as an aging population.
The male to female ratio is the number of males per 100 females in a population. It is usually expressed as a number. The male to female ratio can be used to track changes in the sex ratio of a population, and to identify potential problems such as a shortage of women.
The correct answer is: The number of people per square kilometer.
The other options are incorrect because they do not measure the number of people per unit area.