Here's why:

* Gas: In a gas, molecules are far apart and have very weak attractive forces between them. This allows them to move freely and at high speeds, colliding with each other and the walls of their container.

* Liquid: Liquids have molecules closer together than gases, with stronger attractive forces. This limits their movement, causing them to move more slowly than gas molecules.

* Solid: Solids have the strongest attractive forces and molecules are packed closely together. This restricts movement to vibrations in place, making them the slowest moving of the three states.

In summary: The higher the temperature, the faster the molecules move in any state of matter. However, at the same temperature, gas molecules will always move the fastest.