A student removes a chemical sample from a reagent bottle to be used in an experiment. What should he do with any excess chemical remaining from this sample after the experiment is complete?

he must discard the rest of the sample in an appropriate location, such as discard beakers.

Explanation:

The chemical sample can not be returned to the container because by the time the student removed it, the sample has already begun to react with the environment and the contact with the external environment may have contaminated this sample.

And so, if the student comes back with this leftover sample, they can contaminate the entire sample in the container.