Which of the following oxidation reactions are carried out by both K2Cr2O7 and KMnO4 in acidic medium? (A) I- - I2 (B)…

Both $\ce{K2Cr2O7}$ and $\ce{KMnO4}$ are strong oxidizing agents in acidic medium.

Analysis:

(A) $\ce{I^- -> I2}$: Both $\ce{K2Cr2O7}$ and $\ce{KMnO4}$ oxidize $\ce{I^-}$ to $\ce{I2}$ in acidic medium ✓

(B) $\ce{S^{2-} -> S}$: Both oxidize $\ce{S^{2-}}$ to elemental S in acidic medium ✓

(C) $\ce{Fe^{2+} -> Fe^{3+}}$: Both oxidize $\ce{Fe^{2+}}$ to $\ce{Fe^{3+}}$ in acidic medium ✓

(D) $\ce{I^- -> IO3^-}$: $\ce{KMnO4}$ can oxidize $\ce{I^-}$ to $\ce{IO3^-}$ in acidic medium, but $\ce{K2Cr2O7}$ typically only oxidizes $\ce{I^-}$ to $\ce{I2}$ (not to $\ce{IO3^-}$) ✗

(E) $\ce{S2O3^{2-} -> SO4^{2-}}$: $\ce{KMnO4}$ (alkaline) oxidizes $\ce{S2O3^{2-}}$ to $\ce{SO4^{2-}}$; in acidic medium with $\ce{K2Cr2O7}$, this is less straightforward ✗

From official solution (Image 6): Answer is (c) A, B and C only.

Answer: A, B and C only → Option (c)

Key Points:

• Both $\ce{K2Cr2O7}$ and $\ce{KMnO4}$ (acidic): oxidize $\ce{I^-}\to\ce{I2}$, $\ce{S^{2-}}\to\ce{S}$, $\ce{Fe^{2+}}\to\ce{Fe^{3+}}$
• $\ce{I^-}\to\ce{IO3^-}$: only by $\ce{KMnO4}$ (not $\ce{K2Cr2O7}$)
• $\ce{S2O3^{2-}}\to\ce{SO4^{2-}}$: $\ce{KMnO4}$ in alkaline medium