ANS:D - both (b) and (c)

the total pressure and reducing the temperature affect the relative saturation of a partially saturated mixture of vapor and gas:

1. Increasing the Total Pressure:
   • When the total pressure of a gas-vapor mixture is increased, the partial pressure of the vapor component also increases. This is because the total pressure is the sum of the partial pressures of all components in the mixture, according to Dalton's law of partial pressures.
   • As the partial pressure of the vapor component increases, the driving force for condensation (or vaporization) also increases. This means that more vapor molecules will condense into the liquid phase, leading to an increase in the amount of liquid present in the mixture.
   • Consequently, the relative saturation of the mixture increases because the liquid phase becomes more prevalent relative to the vapor phase. This is because the relative saturation is a measure of the ratio of the actual vapor pressure to the saturation vapor pressure at a given temperature, and an increase in the amount of liquid phase increases the actual vapor pressure.
2. Reducing the Temperature:
   • When the temperature of a gas-vapor mixture is reduced, the saturation vapor pressure of the vapor component decreases. This is because the vapor pressure of a substance is dependent on temperature, with higher temperatures leading to higher vapor pressures.
   • As the saturation vapor pressure decreases, the actual vapor pressure of the vapor component becomes greater than the saturation vapor pressure. This creates a driving force for condensation, causing more vapor molecules to condense into the liquid phase.
   • Similar to the effect of increasing total pressure, reducing the temperature results in an increase in the amount of liquid phase present in the mixture, thereby increasing the relative saturation.