The correct answer is: Nitrous Oxide.
Nitrous oxide is a chemical compound with the formula N2O. It is a colorless, odorless gas that is used as an anesthetic and analgesic. It is also known as laughing gas because it can cause people to laugh uncontrollably when they inhale it.
Carbon monoxide is a colorless, odorless gas that is produced when carbon is burned in an incomplete combustion reaction. It is a toxic gas that can cause death if inhaled in high concentrations.
Sulphur dioxide is a colorless, odorless gas that is produced when sulphur is burned. It is a toxic gas that can cause respiratory problems if inhaled in high concentrations.
Hydrogen peroxide is a colorless liquid that is used as a disinfectant and antiseptic. It is also known as H2O2.
Nitrous oxide is the correct answer because it is the only gas that is known as laughing gas. The other gases are not known as laughing gas.