sand separated from water by filtering water evaporating from a puddle a rock being eroded by wind a nail rusting in water
I gave my students this multiple choice question: Which is an example of a chemical change?

Only one answer is correct among these 4 choices:
- sand separated from water by filtering
- water evaporating from a puddle
- a rock being eroded by wind
- a nail rusting in water

Could you tell me which one is correct?

a nail rusting in water