Sodium hypophosphite (NaPO2H2, also known as sodium phosphinate) is the sodium salt of hypophosphorous acid and is often encountered as the monohydrate, NaPO2H2·H2O. It is a solid at room temperature, appearing as odorless white crystals. It is soluble in water, and easily absorbs moisture from the air.
Sodium hypophosphite should be kept in a cool, dry place, isolated from oxidizing materials. It decomposes into phosphine which is irritating to the respiratory tract and disodium phosphate.