<unk>  is a phosphorus oxoacid and a powerful reducing agent.  Inorganic chemists refer to the free acid by this name (also as "HPA") although its official IUPAC name is phosphinic acid. See Phosphinic acid.  It is a colorless low-melting compound, which is soluble in water, dioxane, and alcohols.  The formula for<unk>  is generally written H3PO2, but a more descriptive presentation is HOP(O)H2 which highlights its monoprotic character.  Salts derived from this acid are called hypophosphites.
HOP(O)H2 exists in equilibrium with the minor tautomer HP(OH)2.  Sometimes the minor tautomer is called<unk>  and the major tautomer is called phosphinic acid.
Hypophosphorous acid
Phosphorous acid
Phosphorus oxoacids
Phosphonic acid
Calcium silicate
Aluminium phosphate
Kaolinite
Phosphate