Is the number of people living in a square mile. in the future, economically developed nations may not have enough money to take care of older citizens due to . in low-income nations, is one reason for the low standard of living.

i) Population density

ii) Under population

iii) Over population

Population density is the number of people living in a square mile. In the future, economically developed nations may not have enough money to take care of older citizens because of underpopulation. In low-income nations, overpopulation is one reason for low standard of living.

so whats the answer? ?