Laughing gas is :

The correct answer is (d). Nitrous oxide is also known as laughing gas. It is a colorless gas with a slightly sweet odor. It is used as an anesthetic and a recreational drug.

(a) Nitrogen dioxide is a reddish-brown gas with a pungent odor. It is a major air pollutant and is a precursor to acid rain.

(b) Dinitrogen tetraoxide is a colorless gas with a choking odor. It is also known as nitrogen tetroxide. It is a strong oxidizer and is used as a rocket propellant.

(c) Carbon dioxide is a colorless, odorless gas that is present in the air. It is a greenhouse gas and is a major contributor to climate change.