Which compound is commonly called laughing gas?

The compound commonly called laughing gas is nitrous oxide.

Nitrous oxide has the chemical formula N₂O, meaning each molecule contains two nitrogen atoms and one oxygen atom. It is a colorless, nonflammable gas with a slightly sweet smell and taste. Its nickname comes from the euphoria or laughter it can sometimes cause when inhaled.

In medicine, controlled nitrous oxide mixtures have been used for analgesia and sedation, especially in dentistry and during childbirth. It is also used as a propellant in whipped-cream dispensers and as an oxidizer in some engines. Medical use requires trained supervision because improper inhalation can cause serious harm.

Nitrous oxide is different from nitric oxide, whose formula is NO. It is also a greenhouse gas, and human activities such as agriculture and combustion contribute to its atmospheric emissions. The gas was first synthesized by English scientist Joseph Priestley in 1772.