Question

A gas can exert pressure on the walls of the container.assign reason

Answer 1

As you know....the molecules of a gas have more kinetic energy...meaning they keep moving easily...just like restless children.SO, in that high energy state, they bump against the walls of the container, and hence apply pressure.                                 
                                                  THE END!!!!!

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.