to observe a color change to get rid of most impurities to identify the boiling point to collect gases for additional study
I gave my students this multiple choice question: A scientist trying to identify an unknown liquid may heat the liquid. Which would be the best reason for the scientist to heat the liquid?

Only one answer is correct among these 4 choices:
- to observe a color change
- to get rid of most impurities
- to identify the boiling point
- to collect gases for additional study

Could you tell me which one is correct?

to identify the boiling point