a metal an atom a compound a nonreactive gas
I gave my students this multiple choice question: The elements sulfur (S) and oxygen combine to form a substance called sulfur dioxide (SO2). Sulfur dioxide is also formed when coal and oil are burned. Sulfur dioxide can best be described as

Only one answer is correct among these 4 choices:
- a metal
- an atom
- a compound
- a nonreactive gas

Could you tell me which one is correct?

a compound