JEE Main 2026 Apr 5 Shift 2, Chemistry Q20: Oxidation and Reduction

JEE Main2026Apr 5, Shift 2Chemistry

A paper dipped in a dilute $H_{2} S O_{4}$ solution of 'X' upon treatment with $S O_{2}$ gas turns into green. The compound 'X' is:

Solution

$S O_{2}$ is a reducing agent. Acidified $K_{2} C r_{2} O_{7}$ (orange) is reduced by $S O_{2}$ to $C r_{2} (S O_{4})_{3}$ , which is green:

$K_{2} C r_{2} O_{7} + 3 S O_{2} + H_{2} S O_{4} \to C r_{2} (S O_{4})_{3} + K_{2} S O_{4} + H_{2} O$ .

The green colour confirms 'X' as $K_{2} C r_{2} O_{7}$ . This is the standard qualitative test for $S O_{2}$ .

Concept behind this question

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