1. Condensation: The gas must first cool down and lose energy. This causes the gas molecules to slow down and move closer together. The attraction between the molecules increases, and they begin to form a liquid.

2. Freezing: As the liquid continues to cool, the molecules slow down even further. Eventually, they become locked in a fixed, rigid structure, forming a solid.

This process is called deposition when it occurs directly from a gas to a solid, skipping the liquid stage.

Here's a breakdown of the changes:

* Gas: Molecules are far apart, move rapidly, and have weak attractions.

* Liquid: Molecules are closer together, move more slowly, and have stronger attractions.

* Solid: Molecules are tightly packed, vibrate in place, and have very strong attractions.

Examples:

* Water vapor (gas) -> Water (liquid) -> Ice (solid)

* Carbon dioxide (gas) -> Dry ice (solid) (deposition)

The exact temperature and pressure required for these changes vary depending on the specific substance.