Here's why:

* Gases: Gas particles have very weak attractive forces between them. They move freely and randomly, colliding with each other and the walls of their container. This results in a lot of space between the particles.

* Liquids: Liquids have stronger attractive forces than gases. The particles are closer together and can move around each other, but they are not as free as gas particles.

* Solids: Solids have the strongest attractive forces. The particles are tightly packed and vibrate in fixed positions.

So, in summary, the further apart the particles are, the weaker the attractive forces between them, and the more likely the substance is to be in a gaseous state.