Hypophosphorous acid (H3PO2) is also named dihydridohydroxidooxidophosphorus, phosphinic acid, or more commonly “HPA”.It is a colorless low-melting compound, which is soluble in water, s. The formula for hypophosphorous acid is generally written H3PO2, but a, more descriptive presentation is HOP(O)H2 which highlights its monoprotic characte.