Question

a gas exerts pressure on the walls of the container.give reason

Answer 1

Hey mate, here is your answer =

The gas exerts the pressure on the walls of the container as when a gas is present in container then it's molecules collide with each other by which a small force exerts on the walls of the container.
Overall, the total sum of the collision of the molecules is the force exert on the walls of the container.

Hope it helps u dear :)

Answer 2

Answer:

The tiny particles of gas collide with walls of container while doing random motion.

Due to this pressure is exerted on walls of container. If temperature of gas is high,  particles move  faster and exert more pressure on walls.