Sound waves need a medium to travel. This means sound can move through solids, liquids, and gases because these states of matter have particles that can vibrate and pass the sound waves along.

- In solids, particles are very close together, so sound travels fastest.
- In liquids, particles are less tightly packed than solids, so sound travels slower than in solids but faster than in gases.
- In gases like air, particles are far apart, so sound travels slower compared to solids and liquids.

However, in a vacuum — which means an empty space with no particles — there is no medium for sound to travel. Because sound requires particles to vibrate and carry the waves, it cannot travel through a vacuum at all.

This is why, for example, in space, which is mostly a vacuum, astronauts cannot hear sounds from outside their spaceships. They need radios or other equipment that convert sound into radio waves, which can travel through space.

So, the correct answer is vacuum, where sound cannot travel because there is no material to carry the vibrations.