A sample of gas is held at constant temperature. The gas is in a container with a moveable piston. The gas is compressed into a small volume. What will happen to the pressure?

The pressure of the gas will increase.

Explanation:

This concept of change in state properties of gas, when compressed in a moveable piston-cylinder assembly, can be explained by using Boyle's law

Boyle's law states that the pressure of a given mass of gas is inversely proportional to its volume given that temperature remains constant.

Following this law, when the gas in the container is compressed to a smaller volume, the pressure will go up.

This is also because the gas is not free to move about without frequent collisions with itself and the walls of the container, due to the resulting smaller space after compression. Therefore, the force it exerts on the walls of the container and the frequency of collision are more.