It is made by reacting ammonia with oxygen with a catalyst. It is also made in lightning. It can be made in small amounts by reacting copper with nitric acid. It can also be made by reducing nitrous acid with compounds such as iron(II) sulfate.
Nitric oxide is used in making nitric acid from ammonia. Ammonia is reacted with air to make nitric oxide, and the nitric oxide is oxidized by air to make nitrogen dioxide. The nitrogen dioxide is dissolved in water to make nitric acid and more nitric oxide.
Nitric oxide is toxic when breathed in. It also easily is oxidized to nitrogen dioxide, a toxic brown choking substance.