Saturation conditions of a substance are determined by which pair of properties?

• A. Temperature and Pressure
• B. Volume and Temperature
• C. Pressure and Humidity
• D. Mass and Temperature

Answer: (A)

Saturation conditions are defined by the temperature and pressure at which liquid and vapor are in equilibrium. For a pure substance, the boundary between liquid and vapor—the coexistence curve on a T–P diagram—maps a specific pressure for each temperature and a specific temperature for each pressure. That means knowing either temperature or pressure sets the state at which the substance is saturated.

Volume, humidity, and mass don’t set that boundary. Volume just scales how much substance you have, humidity describes moisture in air rather than the pure phase boundary, and mass is the amount of substance, not the equilibrium between phases.