Relative humidity changes with temperature.

• A. It changes with temperature
• B. It remains constant regardless of temperature
• C. It is determined solely by altitude
• D. It equals air pressure

Answer: (A)

Relative humidity is a measure of how much water vapor is in the air compared to how much the air can hold at that temperature. The amount the air can hold (its saturation capacity) increases as temperature rises, so the same amount of moisture results in a lower relative humidity when it’s warmer and a higher relative humidity when it’s cooler. If the moisture content stays the same but the temperature increases, the air’s capacity grows and RH falls; if the temperature drops, the capacity shrinks and RH rises toward saturation, potentially producing dew or fog. This is why relative humidity changes with temperature rather than remaining constant, and it isn’t determined solely by altitude or equal to air pressure (RH is a ratio expressed as a percentage of vapor pressure to saturation pressure, not a direct measure of pressure).