The correct option is Dew point.
Explanation
The moisture-holding capacity of air is directly dependent on its temperature. Warmer air can hold more water vapour than colder air. Saturation occurs when the air holds the maximum possible amount of water vapour at a given temperature and pressure.
Option Analysis:
- Latent heat point is incorrect: Latent heat refers to the heat energy absorbed or released during a phase change (e.g., water to vapour) without a change in temperature. It is a form of energy, not a specific temperature point for saturation.
- Dew point is correct: The Dew point is the specific temperature at which a given sample of air becomes saturated. At this temperature, the relative humidity reaches 100%. If the air is cooled below the dew point, the excess water vapour condenses into liquid droplets (dew).
- Freezing point is incorrect: The freezing point is the temperature at which a liquid solidifies (0°C for pure water). While saturation can occur at or below freezing (leading to frost), the general term for the saturation threshold is the dew point.
- Critical temperature is incorrect: Critical temperature is a thermodynamic term referring to the temperature above which a gas cannot be liquefied by pressure alone. It is not relevant to atmospheric moisture saturation.
Key Takeaway: The Dew point is the temperature to which air must be cooled to reach saturation; cooling beyond this point results in condensation.