Which statement about the particle model of matter is correct?

• A. All matter is made of tiny particles
• B. All substances have identical particles
• C. Particles are not moving
• D. The speed of particles decreases with heat

Answer: (A)

Matter is made of tiny particles that are in constant motion. This idea explains why different materials have different properties and behaviors depending on what the particles are like and how they’re arranged. The statement that all matter is made of tiny particles is the accurate one. It’s not true that all substances have identical particles—different materials are composed of different types of particles. Particles aren’t still; they vibrate and move, and their movement is tied to temperature. When you heat something, the particles gain kinetic energy and move faster; cooling slows them down. So the notion that the speed of particles decreases with heat is not correct.