$A$ liquid is in equilibrium with its vapour in a sealed container at a fixed temperature. The volume of the container is suddenly increased.
$a$. What is the initial effect of the change on vapour pressure?
$b$. How do rates of evaporation and condensation change initially?
$c$. What happens when equilibrium is restored finally and what will be the final vapour pressure?

(N/A) . If the volume of the container is suddenly increased,the vapour pressure decreases initially because the same number of vapour molecules are now distributed over a larger volume.
$b$. Since the temperature is constant,the rate of evaporation remains constant. However,the decrease in vapour density leads to a decrease in the rate of collisions of vapour molecules with the liquid surface,so the rate of condensation decreases initially.
$c$. When equilibrium is restored,the rate of evaporation again becomes equal to the rate of condensation. Since the temperature remains constant,the final vapour pressure will be equal to the original vapour pressure,as vapour pressure is a function of temperature only.