ANS:C - decreases with decrease in pressure.

The dew point of a gas-vapor mixture decreases with temperature rise. Explanation:

1. Dew Point:
   • The dew point is the temperature at which air becomes saturated with water vapor, leading to the condensation of water vapor into liquid water (dew) under constant pressure conditions.
   • It represents the temperature at which the relative humidity of the air reaches 100%, indicating that the air is at its maximum moisture-holding capacity and cannot hold any more water vapor.
2. Temperature Rise:
   • When the temperature of a gas-vapor mixture rises, the capacity of the air to hold moisture increases.
   • As the temperature increases, the air molecules gain more kinetic energy, leading to increased molecular motion and greater intermolecular spacing.
   • This increased spacing allows for more water vapor molecules to be accommodated in the air, resulting in a higher moisture-holding capacity.
3. Effect on Dew Point:
   • With an increase in temperature, the air can hold more water vapor before reaching saturation.
   • Therefore, the dew point, which represents the temperature at which saturation occurs, decreases as the air temperature rises.
   • Conversely, a decrease in temperature reduces the moisture-holding capacity of the air, causing the dew point to increase.