The water inside the air represents water vapor, which is water in its gaseous state that exists as individual H₂O molecules mixed with other gases in the atmosphere. Water vapor varies in concentration depending on temperature and location, ranging from nearly 0% in cold, dry regions to about 4% in humid, tropical areas. It is lighter than dry air and plays a key role in weather, climate, and the greenhouse effect by absorbing heat and helping regulate Earth's temperature. Essentially, water vapor is a crucial and variable component of air that influences atmospheric processes and the planet’s energy balance.