The motion of the molecules stops. The motion of the molecules increases. The motion of the molecules decreases. The motion of the molecules is at a constant rate.
I gave my students this multiple choice question: Use The Periodic Table of the Elements and the information below to answer the question. Magnesium metal (Mg) is grayish-white in color and reacts actively with water. Fluorine (F2) is a greenish-yellow gas at room temperature and is a member of the halogen family. These two elements react to produce magnesium fluoride (MgF2), a chemical commonly used in making windows and lenses. How does adding heat energy affect magnesium fluoride (MgF2) molecules?

Only one answer is correct among these 4 choices:
- The motion of the molecules stops.
- The motion of the molecules increases.
- The motion of the molecules decreases.
- The motion of the molecules is at a constant rate.

Could you tell me which one is correct?

The motion of the molecules increases.