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In which of the following reactions, there is change in valency? 4KClO3 → 3KClO4 + KCl SO2 + 2H2S → 2H2O + 3S BaO2 + H2SO4 → BaSO4 + H2O2 3BaO + O2 → 2BaO2

1. 4KClO3 → 3KClO4 + KCl
2. SO2 + 2H2S → 2H2O + 3S
3. BaO2 + H2SO4 → BaSO4 + H2O2
4. 3BaO + O2 → 2BaO2

Correct answer: SO2 + 2H2S → 2H2O + 3S

Solution

In the reaction SO2 + 2H2S → 2H2O + 3S, sulfur undergoes a change in oxidation state: sulfur in SO2 (oxidation state +4) is reduced to elemental sulfur (oxidation state 0), and sulfur in H2S (oxidation state -2) is oxidized to elemental sulfur (oxidation state 0).

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