Any one of three orthophosphates of potassium.

The monobasic form, KH₂PO₄, consists of colorless, water-soluble crystals melting at 253_C; used in sonar transducers, optical modulation, medicine, baking powders, and nutrient solutions; also known as potassium acid phosphate, potassium dihydrogen phosphate (KDP), potassium diphosphate, potassium orthophosphate. The dibasic form, K₂HOP₄, consists of white, water-soluble crystals; used in medicine, fermentation, and nutrient solutions; also known as potassium hydrogen phosphate, potassium monophosphate. The tribasic form, K₃PO₄, is a water-soluble, hygroscopic white powder, melting at 1340_C; used to purify gasoline, to soften water, and to make liquid soaps and fertilizers; also known as neutral potassium phosphate, tripotassium orthophosphate.