Chlorous acid
Its chemical formula is HClO2. It contains chlorite ions. It is not stable. It easily disproportionates to hypochlorous acid and chloric acid. It is a strong oxidizing agent. Chlorites are made by reacting chlorous acid with a base. They are more stable. It can be made by reacting barium chlorite with sulfuric acid. This makes insoluble barium sulfate and chlorous acid.