MCQ
Conjugate acid of $HPO_4^{-2}$ is
- A$H_3PO_4$
- ✓${H_2}PO_4^\Theta $
- C$PO_4^{ - 3}$
- D${H_2}PO_3^\Theta $
$H _2 PO _4^{-} \rightarrow H ^{+}+ HPO _4^{2-}$
The base and its conjugate acid differ by one proton only.
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Reason $R:$ The increasing nuclear charge outweighs the shielding across the period.
In the light of the above statements, choose the most appropriate from the options given below:

| Item $I$ | Item $II$ |
| $A$ Ester test | $P$ Tyr |
| $B$ Carbylamine test | $Q$ Asp |
| $C$ Phthalein dye test | $R$ Ser |
| $S$ Lys |
$E^o (Fe^{+2}, Fe) = -0.44$ $ V$
$E^o (Zn^{+2}, Zn) = -0.76$ $ V$
$E^o (Cu^{+2}, Cu) = +0.34$ $V$
$E^o (Cr^{+2}, Cr) = -0.74$ $V$
$E^o (H^+, 1/2H_2) = -0.00$ $V$