At what pressure does a saturated vapor exist?

A saturated vapor exists when a substance is at the equilibrium state where its vapor pressure equals the surrounding pressure. This condition is heavily influenced by temperature; as the temperature increases, the vapor pressure of a liquid also increases. Therefore, the pressure at which a vapor becomes saturated is not fixed; it changes with temperature.

At any given temperature, there is a specific pressure at which the vapor can exist in equilibrium with its liquid phase. If the surrounding pressure is lower than this saturation pressure, the liquid will start to evaporate until equilibrium is reached. Conversely, if the surrounding pressure exceeds the saturation pressure for that temperature, the vapor will condense back into liquid. Hence, the reason why the correct answer identifies that the pressure varies based on temperature lies in the inherent relationship between temperature, saturation pressure, and the state of the substance involved. This is a fundamental principle in the study of phase transitions and gas laws.