Question

Moist air exerts less pressure than dry air. Why?

Answer 1

Moist air exerts less pressure than dry air because water vapor molecules are lighter than the nitrogen and oxygen molecules they replace in the air. Specifically, water vapor has a molecular weight of about 18 g/mol, which is less than the average molecular weight of dry air (approximately 29 g/mol). When air contains water vapor, it displaces some of the heavier dry air molecules, making the moist air less dense and lighter. As a result, moist air exerts less pressure than dry air of the same volume.