What is the key difference between arithmetic and physiological population density?

Arithmetic is total population divided by total land and physiological is total population divided by total arable land.

Arithmetic population density also known as “real density” is the total number of people divided by the total land area. It doesn’t take account of whether or not the land is rural or urban or whether it is a desert or frozen tundra. It gives a straight forward measurement of people divided by land.

Physiological population density is the number of people per unit area of arable (land suitable for growing crops) land.

All other options (B and C) are wrong.