Arsenite is an ion. Its chemical formula can be either AsO₃^3- or AsO₂^-. It has arsenic in its +3 oxidation state. All arsenites are highly toxic. Sodium arsenite is an example. Arsenites are salts of arsenous acid.

Sometimes arsenite means arsenic trioxide, especially in groundwater chemistry (chemistry dealing with the properties of water in the ground).

• Arsenate
• Arsenide
• Phosphite
• Nitrite

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