Which of the following is known as laughing gas?

1. A

   Ammonia

   Ammonia claims to be the laughing gas, but it is a pungent, toxic compound widely used in fertilizers rather than inducing laughter. Therefore, this option is incorrect.

2. B

   Nitrous Oxide

   Nitrous oxide claims to be the correct answer because it is a chemical compound with the formula N2O, commonly known as laughing gas due to its euphoric effects when inhaled. It is widely used in surgery and dentistry for its anaesthetic and pain-reducing properties, making this the official key.

3. C

   Carbon Monoxide

   Carbon monoxide claims to be the laughing gas, but it is actually a colorless, odorless, and highly toxic gas produced by incomplete combustion. Hence, this option is incorrect.

4. D

   Chlorofluorocarbon

   Chlorofluorocarbon claims to be the laughing gas, but these are organic compounds containing carbon, chlorine, and fluorine historically used as refrigerants and aerosol propellants. Thus, this option is incorrect.

Summary. Official key is (b) Nitrous Oxide. This question tests the common chemical names and general awareness of standard laboratory gases. Nitrous oxide was discovered by the English scientist Joseph Priestley and is well known for its inhalation effects. The other options represent entirely different industrial and chemical substances with distinct properties and hazards. Therefore, option (b) is the only correct choice.