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Question: Answered & Verified by Expert
Conjugate base of $\mathrm{H}_{2} \mathrm{PO}_{4}^{-}$is
ChemistryIonic EquilibriumKCETKCET 2013
Options:
  • A $\mathrm{HPO}_{4}^{-}$
  • B $\mathrm{HPO}_{4}^{2-}$
  • C $\mathrm{H}_{3} \mathrm{PO}_{4}$
  • D $\mathrm{PO}_{4}^{3-}$
Solution:
1191 Upvotes Verified Answer
The correct answer is: $\mathrm{HPO}_{4}^{2-}$
A conjugate pair of acid and a base differs by a proton only, i.e.,
conjugate acid $\rightleftharpoons$ conjugate base $+\mathrm{H}^{+}$
$\mathrm{H}_{2} \mathrm{PO}_{4}^{-} \rightleftharpoons \mathrm{HPO}_{4}^{2-}+\mathrm{H}^{+}$
Thus, $\mathrm{H}_{2} \mathrm{PO}_{4}^{-}$can give a proton and hence is an acid while $\mathrm{HPO}_{4}^{2-}$ can accept the proton and hence is a base.

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