Item SC071003: The surface of a copper penny changing color after being in a drawer for years is an example of a chemical reaction.

Which of the following is an example of a chemical reaction?

  1. Aluminum foil being cut into smaller pieces
  2. A drop of food coloring dissolving in water
  3. Melted butter becoming a solid when placed in the refrigerator
  4. The surface of a copper penny changing color after being in a drawer for years