VAPOUR IS SAID TO BE SATURATED ON TOP OF AN ENCLOSED LIQUID IF

• A. The rate of condensation is greater than that of vapourization
• B. The rate of condensation is equal to that of vapourization ✓
• C. There is neither condensation nor vaporization of the liquid
• D. The rate of condensation is less that that of vaporization

The answer to the question is: B. The rate of condensation is equal to that of vapourization

When a vapor is said to be saturated on top of an enclosed liquid, it means that the rate of condensation is equal to the rate of vaporization. This state is known as equilibrium, where the liquid and vapor phases coexist without any net change in the amount of each phase. The saturation vapor pressure is the pressure exerted by a vapor when it is in equilibrium with its condensed phase. At this point, the vapor is said to be saturated because it cannot hold any more molecules in the gas phase at that temperature.

The condition of saturation occurs when the rate of condensation equals the rate of evaporation. At this point, the number of molecules leaving the liquid surface is equal to the number returning to it. This balance between condensation and evaporation results in a constant concentration of vapor above the liquid. If the rate of condensation were greater than that of evaporation, then the vapor would not be saturated; instead, it would be in a state of supersaturation, which is unstable and would lead to excess molecules returning to the liquid phase until equilibrium is reached. Conversely, if the rate of evaporation were greater than that of condensation, then there would be no saturation as the concentration of vapor above the liquid would continue to increase.

In summary, when a vapor is saturated on top of an enclosed liquid, it means that the rates of condensation and vaporization are equal, resulting in a state of equilibrium where no net change occurs in the amount of each phase.