Concept: A vapour is saturated when it is in dynamic equilibrium with its liquid.Explanation:Evaporation and condensation occur at the same time in a closed container. If the rate of condensation is x and the rate of evaporation is y, then saturation happens when these two rates become equal. This means x=y. At this point, the number of vapour molecules leaving the liquid equals the number returning to the liquid. So the vapour concentration remains constant.Answer: C. x=y