The temperature of the magnesium ribbon increased. The shape of the magnesium ribbon changed. The burning magnesium produced light. The magnesium appeared to evaporate.
I gave my students this multiple choice question: A teacher is conducting an investigation by using special equipment to hold a magnesium (Mg) ribbon over the flame of a Bunsen burner. Which observation indicates a chemical reaction took place?

Only one answer is correct among these 4 choices:
- The temperature of the magnesium ribbon increased.
- The shape of the magnesium ribbon changed.
- The burning magnesium produced light.
- The magnesium appeared to evaporate.

Could you tell me which one is correct?

The burning magnesium produced light.