Explain the following:
$(i)$ Gases exert pressure on the walls of the container.
$(ii)$ Water is liquid at room temperature.
$(iii)$ Evaporation causes cooling.

(N/A) $(i)$ Gas particles move randomly at high speeds and collide with the walls of the container,exerting force per unit area,which is perceived as pressure.
$(ii)$ Water is a liquid at room temperature because its melting point is below room temperature $(0 \ ^\circ C)$ and its boiling point is above room temperature $(100 \ ^\circ C)$.
$(iii)$ During evaporation,particles of the liquid absorb energy from the surroundings to overcome the forces of attraction and change into the vapor state. This loss of energy from the surroundings results in a cooling effect.