Nitrous acid
Nitrous acid is a chemical compound. It is a weak acid. Its chemical formula is HNO2. It is unstable. It is made by reacting a strong acid with sodium nitrite. It is a light blue solution. It breaks down to make nitric oxide, nitrogen dioxide, and water when it is concentrated. Nitrogen dioxide can be reacted with water to make a mixture of nitrous acid and nitric acid. It is used to make chemicals.