Explain, in terms of the behaviour of molecules, how a gas exerts a pressure on the walls of its container. (4)

This question is 4 marks so you need to make at least 4 points.

These types of questions just require memorising the 4 points:

Lots of molecules collide with the walls.

The molecules change momentum as they collide with the walls.

Force is the rate of change of momentum.

Pressure = force/area.

Remember these 4 points and you'll get full marks for the question.