ANS:D - none of these.

The relative saturation of an unsaturated mixture of gas and vapor refers to the degree of saturation of the vapor phase relative to its saturation point at the given temperature and pressure. It is defined as the ratio of the partial pressure of the vapor in the mixture to the saturation vapor pressure of the pure substance at the same temperature. The relative saturation of an unsaturated mixture is indeed independent of the nature of the vapor, as it only depends on the partial pressure of the vapor in the mixture and the saturation vapor pressure of the pure substance at the given temperature. Similarly, it is independent of the composition of the mixture because it is determined solely by the partial pressure of the vapor. However, the relative saturation of an unsaturated mixture is dependent on the temperature of the mixture because the saturation vapor pressure of the pure substance is temperature-dependent. As the temperature changes, the saturation vapor pressure changes, thereby affecting the relative saturation of the mixture. So, the correct answer is: temperature of the mixture.