Question

show that liquid exerts pressure on the walls of the container

Answer 1

If you have liquid on earth it generates a pressure ( see ) which is dependent on the density of the liquid, the force of gravity and the height of the liquid.

If you place an object in liquid it gets buoyancy (can be explained as the difference of pressure at the bottom and top of the object) and if the buoyancy is higher than earth's gravitational force which pulls the object down it will float at the surface...

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.