Concept:Saturated vapour exists when the vapour is in dynamic equilibrium with its liquid.Explanation:In a closed container, molecules escape the liquid and vapour molecules return to the liquid continuously.When the vapour is saturated, the rate of condensation equals the rate of vapourization and the vapour pressure becomes constant.Therefore, the correct condition is that condensation rate is equal to vapourization rate.Answer:B. The rate of condensation is equal to that of vapourization