In a double covalent bonds there are 4 valence electrons that are shared.
The ionic compound of FePO4 is the iron III phosphate. Or you can call it ferric phosphate or ferric orthophosphate.
Just for general informations, It's normally used in steel and metal manufacturing processes, in organic farming, and many other uses.
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(2) a base because they accept H+ ions. NH3 is the conjugate base of NH4+.
