The gas is more dense than the air. The gas is more visible than the air. The gas smells different from the air. The gas evaporates faster than the air.
I gave my students this multiple choice question: During a demonstration, a teacher pours CO_{2} gas over a candle, putting out the flame. Which physical property allows the teacher to pour the CO_{2} gas?

Only one answer is correct among these 4 choices:
- The gas is more dense than the air.
- The gas is more visible than the air.
- The gas smells different from the air.
- The gas evaporates faster than the air.

Could you tell me which one is correct?

The gas is more dense than the air.