Sound cannot travel through:

**The reasoning** Sound is a **mechanical wave** — it travels by vibrating particles (molecules or atoms) that bump into each other, passing energy along. In air, water, or steel, there are plenty of particles to vibrate. But in a **vacuum**, there are *no particles at all* — it's completely empty space. No particles means nothing to vibrate, so sound waves literally have nothing to travel through. That's why in space (which is mostly vacuum), even massive explosions happen in total silence! **Why the wrong options tempt you** - **A) Air** — You hear sounds daily through air, so this seems obviously wrong - **B) Water** — This tricks students who forget whales communicate underwater, or that you can hear splashes beneath the surface - **D) Steel** — Many think solid materials block sound, but metals actually carry sound *faster* than air (particles are closer together!) **Quick takeaway** Remember: **Sound needs matter to travel** — if there's no particles (vacuum), there's no sound, which is why astronauts use radios even when standing next to each other in space.