achiever GC Question, Plz help

[far123]

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What is the conjugate base of H3PO4?

A.PO43-B.HPO42-C.H2PO4-D.H3O+E.H2O
I guess both A, and B answers are right, what am I missing?

 

[Hugh Mannity]

I would say C. Remove only 1 proton. CB of C is B and CB of B is A.

 

[far123]

thanks, is it always like this? I mean just one H at the time?

 

[osimsDDS]

These are polyprotic (more than 1 H+), if you have for example HCl its conjugate base would be Cl- (just 1 H+), also it is a strong acid so its CB would be a weak base...thats pretty important to note