Which of the gases is employed as an anaesthesia?

Analyze the question: The question asks which gas is used as an anaesthetic, meaning a substance that numbs pain or induces unconsciousness during medical procedures.

Explain the concept: Nitrogen forms several oxides, and each has different properties and uses:

| Formula | Name | Key property/use | |---|---|---| | N₂O | Dinitrogen monoxide (nitrous oxide) | Mild anaesthetic, known as "laughing gas" | | NO | Nitrogen monoxide (nitric oxide) | Colourless gas that turns brown in air; not an anaesthetic | | NO₂ | Nitrogen dioxide | Brown, toxic, poisonous gas; contributes to acid rain | | NH₃ | Ammonia | Pungent gas used for fertilizers and in the Haber process; irritating to inhale |

Step-by-step solution:

1. Option B (NO₂) is a toxic, choking brown gas, so it cannot be used for anaesthesia.
2. Option C (NH₃) has a sharp, irritating smell and is used in fertilizers and cleaning agents, not in medicine for anaesthesia.
3. Option D (NO) is reactive and toxic at high concentrations, and it is not used as an anaesthetic.
4. Option A (N₂O) is non-toxic in controlled doses, and it is used in dentistry and minor surgery. It is also called laughing gas because it produces mild euphoria. It is usually mixed with oxygen for safe use.

Answer: The correct option is A. N₂O.

Exam tip: Remember "N₂O = laughing gas = anaesthetic." Also, N₂O is the gas used as a propellant in whipped cream cans, which is another common JAMB question about it.