Water, rust, and salt are atoms. Water, rust, and salt are mixtures. Water, rust, and salt are elements. Water, rust, and salt are compounds.
I gave my students this multiple choice question: Which of the following do water (H2O), rust (Fe2O3), and salt (NaCl) have in common?

Only one answer is correct among these 4 choices:
- Water, rust, and salt are atoms.
- Water, rust, and salt are mixtures.
- Water, rust, and salt are elements.
- Water, rust, and salt are compounds.

Could you tell me which one is correct?

Water, rust, and salt are compounds.