Sound needs a:

**The reasoning** Sound is a **mechanical wave** — it travels by making particles vibrate and bump into their neighbors. Think of it like a "push" passing through a crowd: each person nudges the next. For this to work, you need *something* with particles that can vibrate — that "something" is called a **medium**. The medium can be: - **Solid** (sound travels through walls, your desk) - **Liquid** (you can hear underwater) - **Gas** (sound travels through air to your ears) No particles? No sound. That's why astronauts in space can't hear each other scream — space is a vacuum with no medium. **Why the wrong options tempt you** - **A) Vacuum** — This is the *opposite* of what sound needs. Space is silent! - **C) Heat** — Temperature affects sound *speed*, but isn't required for sound to exist - **D) Light** — Light is an electromagnetic wave that *doesn't* need a medium; sound does **Quick takeaway** "Sound waves need particles to vibrate — no medium, no sound; that's why space is silent."