The properties of both sodium and chlorine change. The properties of both sodium and chlorine remain the same. The properties of sodium are different but chlorine remains a dangerous gas. The properties of sodium remain the same but the properties of chlorine change.
I gave my students this multiple choice question: Sodium (Na) and chlorine (Cl) are two reactive and dangerous elements. Chlorine is a halogen gas that can cause respiratory damage and sodium is an alkali metal that reacts violently with water. What happens to the properties of sodium and chlorine when they react to form sodium chloride (NaCl), common table salt?

Only one answer is correct among these 4 choices:
- The properties of both sodium and chlorine change.
- The properties of both sodium and chlorine remain the same.
- The properties of sodium are different but chlorine remains a dangerous gas.
- The properties of sodium remain the same but the properties of chlorine change.

Could you tell me which one is correct?

The properties of both sodium and chlorine change.