JEE Advanced Chemistry question

Which of the following can convert acidified Cr2O7²⁻ to green?

(A)SO2/H2SO3/H2SO4
(B)SO3/H2SO3/H2S
(C)SO3²⁻/H2S/Fe²⁺Correct
(D)S2O3²⁻/SO3/Fe³⁺

Answer: (C)

Solution

Acidified orange Cr2O7²⁻ turns green when reduced to Cr³⁺, so the listed species must all be reducing agents capable of this reduction: SO3²⁻ + Cr2O7²⁻ → SO4²⁻ + Cr³⁺, H2S + Cr2O7²⁻ → S + Cr³⁺, and Fe²⁺ + Cr2O7²⁻ → Fe³⁺ + Cr³⁺

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Question ID VK-159312