Here's why:

* Solids: Molecules in solids are packed tightly together. This allows sound vibrations to transfer quickly and efficiently from one molecule to the next.

* Liquids: Molecules in liquids are closer together than in gases, but not as tightly packed as in solids. This means sound travels faster in liquids than in gases, but slower than in solids.

* Gases: Molecules in gases are spread far apart. Sound vibrations take longer to transfer between molecules, making sound travel slowest in gases.

In summary:

* Fastest: Solids

* Medium: Liquids

* Slowest: Gases