Identify the oxidation reaction in which acidified KMnO ₄ is required

Step-by-step solution

KMnO₄ acts as an oxidising agent whose products depend on the medium. In acidic medium: MnO₄^- is reduced to Mn²⁺ . It oxidises I^- to I₂ : 2MnO₄^- + 10I^- + 16H^+ 2Mn²⁺ + 8H₂O + 5I₂ — requires acidified KMnO₄ . Options (2), (3), and (4) occur in neutral or faintly alkaline medium where MnO₄^- is reduced to MnO₂ , not in acidic medium. Only the conversion of iodide ions to iodine specifically requires acidified KMnO₄ .