I would like to have clarity on how air accommodates water. When water vaporises, does the water molecules just squeeze into the space between already existing molecules of nitrogen and oxygen? From Avogadro's principle, I expect that water molecules are supposed to replace air molecules rather than just being added to the bunch. The fact that humid air is less dense seems to support this. But many of the scientific articles I read seem to imply the more intuitive 'squeezing in picture' especially those explaining why hot air can hold more water than colder air. Are they just wrong? Or am I missing anything equally relevant here?
The water molecules penetrate between the air molecules, after which the air pressure is a little increased. This increased pressure makes some airflow outward (away from the liquid water from which the water molecules arise), so the Avogadro number is maintained. As a result, air that contains many water molecules will have a smaller mass density than air with less water molecules (because the other components of air have a higher mass than water molecules).