A different mixture is formed in each case. A different solution is formed in each case. Both a change of state and of elements is involved. New molecules are formed but the same elements exist.
I gave my students this multiple choice question: Oxygen reacts with iron to produce rust and with hydrogen to produce water. Which statement describes both reactions?

Only one answer is correct among these 4 choices:
- A different mixture is formed in each case.
- A different solution is formed in each case.
- Both a change of state and of elements is involved.
- New molecules are formed but the same elements exist.

Could you tell me which one is correct?

New molecules are formed but the same elements exist.