According to one theory, the pressure of a gas increases as its volume decreases, because the molecules in the gas have to move a shorter distance to hit the walls of the container. does this theory follow
a.) macroscopic or
b.) microscopic description of chemical behavior?

The theory follow a microscopic description of chemical behavior.

Explanation:

The volume decrease is a macroscopic observation that can be explained by a microscopic event.

The molecules that make the gas are invisible to the human eye, however, the way they behave are the reason for different properties of the gas. It is easy to understand this if we think about the gas molecules as moving balls in a box. If we take the same amount of balls to a smaller box (decreasing the volume), the balls will hit the walls of the box easier (increasing the pressure).