Adiabatic saturation of unsaturated air: identify the quantity that remains constant During an adiabatic saturation process applied to unsaturated air (idealized psychrometric analysis), which standard air property stays essentially constant? Choose the correct option.

Approach
In the ideal adiabatic saturation process (no heat/work interactions with surroundings; negligible KE/PE changes), the air-vapor mixture follows an approximately constant wet-bulb temperature (and constant enthalpy) path on the psychrometric chart.

Eliminations
Relative humidity varies as the state approaches saturation.Dew-point and dry-bulb temperatures change during adiabatic humidification.

Final Answer
Wet-bulb temperature remains essentially constant.