When is vapor said to be saturated?

Vapor is considered saturated when the rates of evaporation and condensation are equal in a closed container. At this state, the air (or space above the liquid) is holding the maximum amount of vapor at a given temperature and pressure, meaning that the vapor cannot increase further without either increasing the temperature or pressure within the container.

This saturation point indicates a dynamic equilibrium where molecules are continuously evaporating into the vapor phase while simultaneously condensing back into the liquid phase at the same rate, leading to no net change in the quantity of vapor present. This concept is key in understanding phase changes and the behavior of substances under different conditions of temperature and pressure.

The notion of saturation does not necessarily relate to the boiling point or reaching a maximum temperature; those states may indicate changes occurring rather than a balance between evaporation and condensation. Thus, the condition of equilibrium defined in option B captures the essence of vapor saturation accurately.