According to the kinetic theory of gases, the pressure exerted by a gas on the walls of its container is directly caused by:
the gravitational attraction between the gas molecules and the container walls.
the rate of change of momentum of the gas molecules as they collide with and rebound from the walls.
the loss of kinetic energy of the gas molecules during elastic collisions.
the collisions between the gas molecules themselves within the volume of the container.
151 exam-style questions on CIE IGCSE Physics 2.1.2a Particle structure and motion in solids, liquids and gases. Each one has a worked solution and a mark scheme showing where the marks go.