Phosphorous acid is an inorganic compound with the chemical formula H?PO?, appearing as colorless to pale yellow ice-like crystals^[3

], which are readily soluble in water and ethanol. It slowly oxidizes to phosphoric acid in air and decomposes into phosphoric acid and phosphine when heated to 180°C. It is primarily used as a raw material in the production of plastic stabilizers and also in the manufacture of synthetic fibers and phosphites.