a compound. a mixture. a solution. an element.
I gave my students this multiple choice question: A researcher uses several procedures to separate a rock sample into different chemicals. A mass of 50 grams of one chemical is produced. If this chemical cannot be separated into other chemicals, then it is best described as

Only one answer is correct among these 4 choices:
- a compound.
- a mixture.
- a solution.
- an element.

Could you tell me which one is correct?

an element.