* Sound is a mechanical wave: This means it needs a medium (like air, water, or a solid) to travel. Sound waves are vibrations that travel through the particles of a medium.

* Density and Elasticity: The speed of sound is determined by the density and elasticity of the medium.

* Density: Denser materials have particles closer together, allowing vibrations to transfer more quickly.

* Elasticity: Elastic materials (like solids) can quickly return to their original shape after being deformed, facilitating sound transmission.

Let's compare the options:

* Solids: Have the highest density and elasticity, leading to the fastest sound transmission.

* Liquids: Have a lower density and elasticity than solids, so sound travels slower.

* Gases: Have the lowest density and elasticity, resulting in the slowest sound transmission.

* Vacuum: A vacuum has no particles, so sound cannot travel through it.

In summary: The tighter the particles are packed together and the more elastic the material, the faster sound will travel.