Give reasons for the following:
$(i)$ $A$ gas exerts pressure on the walls of the container.
$(ii)$ $A$ gas fills the vessel in which it is kept.

(N/A) $(i)$ The molecules of a gas are in constant,random motion in all directions. As they move,they collide with each other and strike the walls of the container,exerting a force per unit area,which is perceived as pressure.
$(ii)$ The force of attraction between the particles of a gas is negligible,and the particles possess high kinetic energy. This allows them to move freely and occupy all the available space in the vessel in which they are kept.