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A white or yellowish hygroscopic crystalline solid, H3PO3, used as a reducing agent and to produce phosphite salts.
1. (Elements & Compounds) Also called: orthophosphorous acid a white or yellowish hygroscopic crystalline dibasic acid. Formula: H3PO3. Systematic name: phosphoric acid
2. (Elements & Compounds) any oxyacid of phosphorus containing less oxygen than the corresponding phosphoric acid
a colorless, crystalline, water-soluble acid of phosphorus, H3PO3, from which phosphites are derived.