Question

How deos the air on a hot day compare with the air on a cold day?

Answer 1

On a hot day, the air particles are farther away from each other, and moving very quickly, bouncing off of one another.  On a cold day, the particles are more compact and move much less quickly.

Answer 2

Air on a hot day translates to hot air and air on a cold day translates to cold air.

The hot air usually have more energy due to particles being more excited by the heat. They are usually less dense too. The cold air is usually more dense and have less energy.

The hot air also has more capacity to hold water moisture while cold air has less capacity to hold water moisture.