JEE Main 2025 Jan 28 Shift 1, Chemistry Q19: Oxidation and Reduction

JEE Main2025Jan 28, Shift 1Chemistry

Which of the following oxidation reactions are carried out by both K $_{2}$ Cr $_{2}$ O $_{7}$ and KMnO $_{4}$ in acidic medium ?

A. $I^{-} \to I_{2}$
B. $S^{2 -} \to S$
C. $Fe^{2 +} \to Fe^{3 +}$
D. $I^{-} \to IO_{3}^{-}$
E. $S_{2} O_{3}^{2 -} \to SO_{4}^{2 -}$

Choose the correct answer from the options given below :

A
B, C and D only
B
A, D and E only
C
A, B and C only
D
C, D and E only

Solution

In acidic medium both K $_{2}$ Cr $_{2}$ O $_{7}$ and KMnO $_{4}$ are mild-to-moderate oxidants that carry out:

A. $2 I^{-} \to I_{2} + 2 e^{-}$ ✓ (both)
B. $S^{2 -} \to S + 2 e^{-}$ ✓ (both)
C. $Fe^{2 +} \to Fe^{3 +} + e^{-}$ ✓ (both)

Reactions D and E require a strongly alkaline (or much stronger oxidising) environment to push iodide all the way to iodate, and to oxidise thiosulphate all the way to sulphate; these are not the standard products with acidic K $_{2}$ Cr $_{2}$ O $_{7}$ / KMnO $_{4}$ .

$∴$ A, B and C only.

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JEE Main 2025 Jan 28 Shift 1, Chemistry Q19: Oxidation and Reduction

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