ANS:A - termed as relative saturation.

The percentage ratio of the partial pressure of the vapor to the vapor pressure of the liquid at the existing temperature is termed as percentage saturation. This concept is important in understanding the vapor-liquid equilibrium of a system. When a liquid is in equilibrium with its vapor at a given temperature, the partial pressure of the vapor is equal to the vapor pressure of the liquid at that temperature. The percentage saturation indicates how close the system is to this equilibrium condition. It's worth noting that the percentage saturation is not a function of the composition of the gas mixture or the nature of the vapor. Instead, it solely depends on the partial pressure of the vapor and the vapor pressure of the liquid at the given temperature. Therefore, the statement "called percentage saturation" correctly describes the concept.