Nitrogen monoxide, also known as nitric oxide, is a colorless gas with the molecular formula NO. Its molar mass is 30.01 grams per mole, and it has a density of 1.34 grams per cubic decimeter. Its melting point is -263 degrees Fahrenheit, and its boiling point is -242 degrees Fahrenheit.
Nitric oxide is classified as a free radical. It is an intermediate in several processes in the chemical industry. It is also produced during lightning and during combustion reactions in fossil fuel plants or automobile engines. Nitric oxide reacts with molecular oxygen to produce nitrogen dioxide, NO2. In an aqueous solution, it reacts with molecular oxygen and water to produce nitrous acid, HNO2.