Hypophosphoric acid is a mineral acid with the formula H4P2O6, with phosphorus in a formal oxidation state of +4. In the solid state it is present as the dihydrate, H4P2O6·2H2O. In hypophosphoric acid the P atoms are identical and joined directly with a P-P bond. There is an isomeric form isohypophosphoric acid which has a different structure wit...
[n] - a crystalline tetrabasic acid (H4P2O6)
a tetrabasic acid, HPO, produced by the slow oxidation of phosphorous in moist air.