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Meaning of orthophosphorous acid

or'tho•phos'pho•rous ac'id

Pronunciation: (ôr'thu-fos'fur-us, ôr"thō-fos-fôr'us, -fōr'-), [key]
— Chem. Chem.
  1. a white to yellowish, crystalline, hygroscopic, water-soluble solid, HPO, used chiefly in the synthesis of phosphites.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.