In basic medium, H₂O₂ exhibits which of the following reactions?
(A) Mn²⁺ → Mn⁴⁺
(B) I² → I⁻
(C) PbS → PbSO₄
Choose the most appropriate answer from the options given below :

Solution

Chemistry ma’am · 3 steps

In base, H₂O₂ works both ways: it oxidises Mn²⁺ and reduces I₂.

1. Two roles. In H₂O₂ oxygen is at -1, between -2 and 0. So H₂O₂ can be reduced to H₂O (oxidising agent) or oxidised to O₂ (reducing agent). Which role it plays depends on the medium and on the partner.

   Change	Oxidation state	Role of H₂O₂	Medium
   (A) Mn²⁺ → MnO₂	Mn: +2 → +4	oxidising agent	basic
   (B) I₂ → I⁻	I: 0 → -1	reducing agent	basic
   (C) PbS → PbSO₄	S: -2 → +6	oxidising agent	acidic

2. Basic medium equations. Mn²⁺ + H₂O₂ + 2OH⁻ → MnO₂ + 2H₂O and I₂ + H₂O₂ + 2OH⁻ → 2I⁻ + 2H₂O + O₂. Both need OH⁻, so both are basic-medium reactions.
3. So. The oxidation of PbS to PbSO₄ is listed among the acidic-medium reactions, so only (A) and (B) fit. The answer is (b).

The idea to keep. Learn H₂O₂ reactions in four boxes: oxidising or reducing, in acid or in base. In base it reduces I₂ to I⁻ and oxidises Mn²⁺ to MnO₂.

Answer from the NTA final answer key. Solution by PrepWiser.