Explanation:

Alright, let’s break these down quickly:

- Option 1: Carbon dioxide—That’s the gas in your soda, not what makes you laugh.

- Option 2: Nitrogen oxide—Actually, laughing gas is nitrous oxide, not nitrogen oxide. Nitrogen oxide is a different compound altogether.

- Option 3: Carbon monoxide—Dangerous stuff, but it won’t make you giggle. It’s a silent, poisonous gas.

- Option 4: Sulphur dioxide—That’s what gives a sharp smell to burnt matches and industrial pollution. Again, no laughter here.

The correct answer is:

Nitrous oxide (commonly called laughing gas) is what dentists sometimes use to help people relax. For this question, none of the options exactly match “nitrous oxide,” but option 2, Nitrogen oxide, is close, although technically imprecise.