Pour the acid into a trash can. Neutralize the acid before pouring it down a sink. Return the acid to the teacher's stock bottle. Allow the water to evaporate from the acid solution.
I gave my students this multiple choice question: In science class, a student obtains 20 mL of an acid solution. A small amount of acid is added to a substance to detect the presence of copper. What should be done with the excess acid solution?

Only one answer is correct among these 4 choices:
- Pour the acid into a trash can.
- Neutralize the acid before pouring it down a sink.
- Return the acid to the teacher's stock bottle.
- Allow the water to evaporate from the acid solution.

Could you tell me which one is correct?

Neutralize the acid before pouring it down a sink.