As a substance gets cooler, what happens to the molecules within it?

• A. The molecules increase in size.
• B. The molecules move more slowly and have less kinetic energy.
• C. The molecules gain electrons.
• D. The molecules move more quickly and have more kinetic energy.

Answer: (B)

Verified step by step guidance

1. Understand that temperature is a measure of the average kinetic energy of molecules in a substance.
2. Recall that as a substance cools, its temperature decreases, which means the average kinetic energy of its molecules decreases.
3. Recognize that kinetic energy is related to the speed of molecular motion; lower kinetic energy means molecules move more slowly.
4. Note that molecular size does not increase or decrease significantly with temperature changes; instead, the motion and energy of molecules change.
5. Conclude that as a substance gets cooler, the molecules move more slowly and have less kinetic energy.