Question

how the gas exerts pressure on the walls of the container

Answer 1

The molecules are continually colliding with each other and with the walls of the container. When a molecule collides with the wall, they exert small force on the wall The pressure exertedby the gas is due to the sum of all these collision forces.The more particles that hit the walls, the higher the pressure.

Answer 2

Because in the gaseous state, the particles move about randomly at high speed. Due to this random movement, the particles hit each other and also the walls of the container. The pressure exerted by the gas is because of this force exerted by gas particles per unit area on the walls of the container.