The nitrite ion, which has the chemical formula NO−2, is a symmetric anion with equal N–O bond lengths. Upon protonation, the unstable weak acid nitrous acid is produced. Nitrite can be oxidized or reduced, with the product somewhat dependent on the oxidizing/reducing agent and its strength. The nitrite ion is an ambidentate ligand and is known to bond to metal centers in at least five different ways.

2 group is present in nitrous acid esters and nitro compounds. Nitrite (mostly sodium nitrite) is also used in the food production industry for curing meat.

Nitrate or nitrite (ingested) under conditions that result in endogenous nitrosation has been classified as "Probably carcinogenic to humans" (Group 2A) by International Agency for Research on Cancer (IARC), the specialized cancer agency of the World Health Organization (WHO) of the United Nations.

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