Which of the following is not a conjugate acid base pair?

Options

A. `HPO_(3)^(2-), PO^(3-)_(3)`
B. `H_(2)PO_(4)^(-), HPO_(4)^(2-)`
C. `H_(2)PO_(4)^(-),H_(3)PO_(4)`
D. `H_(2)PO_(4)^(-), PO_(3)^(3-)`

Answer

D

Explanation

A conjugate acid-base pair differs by a single proton.
`HPO^(2-)_(3) + H_(2)O hArr H_(3)O^(+) + PO^(2-)_(3)`
`H_(2)PO^(-)_(4) + H_(2)O hArr H_(3)O^(+) + HPO^(2-)_(4)`
`H_(3)PO_(4) + H_(2)O hArr H_(3)O^(+) + H_(2)PO^(-)_(4)`