JEE Main 2025 · 22 January · evening · Single correct · +4 / −1
The species which does not undergo disproportionation reaction is :
- (a) ClO₄⁻
- (b) ClO₃⁻
- (c) ClO⁻
- (d) ClO₂⁻
Answer and solution
Answer (a) ClO₄⁻
Solution
Chemistry ma’am · 3 steps
To disproportionate, chlorine must be able to go both up and down. Check the oxidation state first.
- What disproportionation needs. In disproportionation, one element is oxidised and reduced at the same time. So it must sit in an intermediate oxidation state, with room to rise and room to fall.
- Chlorine's range. Chlorine goes from -1 (in Cl⁻) to +7, its highest. A chlorine atom already at +7 cannot be oxidised any further.
Species Oxidation state of Cl Can go up and down? ClO₄⁻ +7, the maximum No, it can only be reduced ClO₃⁻ +5 Yes: 4ClO₃⁻ → 3ClO₄⁻ + Cl⁻ ClO⁻ +1 Yes: 3ClO⁻ → 2Cl⁻ + ClO₃⁻ ClO₂⁻ +3 Yes: 3ClO₂⁻ → 2ClO₃⁻ + Cl⁻ - So. Only ClO₄⁻ has chlorine in its highest oxidation state, so it cannot disproportionate. The answer is (a).
The idea to keep. An element at its highest or lowest oxidation state can never disproportionate. Only an intermediate state can split into one higher and one lower state.
Answer from the NTA final answer key. Solution by PrepWiser.