What is the relationship between air density and moisture content?

Moist air is less dense than dry air because the presence of water vapor in the air displaces some of the heavier nitrogen and oxygen molecules. Each molecule of water vapor (H₂O) has a molecular weight of approximately 18 g/mol, while nitrogen (N₂) and oxygen (O₂) have molecular weights of about 28 g/mol and 32 g/mol, respectively. When water vapor enters the atmosphere, it replaces some of these heavier molecules, leading to a decrease in overall air density.

This concept is crucial in meteorology because it affects various atmospheric processes, such as buoyancy, stability, and weather patterns. Understanding this relationship helps meteorologists predict phenomena such as cloud formation, precipitation, and storm development. The other options do not accurately describe the relationship between air density and moisture content, as they either misrepresent the role of moisture or misunderstand the principles of density in gases.