Hypophosphite, also known as phosphonate, is an ion. Its chemical formula is HPO. It contains phosphorus in its +1 oxidation state. It is made by disproportionation of phosphorus in warm alkali. Phosphine is also produced. It is a strong reducing agent. Chemical compounds that contain the hypophosphite ions are called hypophosphites. They are poisonous. Hypophosphites are salts of hypophosphorous acid.