Identifying Oxidizing and Reducing Agents from Color Changes

Steps:

• Acidified potassium manganate(VII) (KMnO4) is a purple oxidizing agent reduced to colorless Mn²⁺ by reducing agents.
• Gas X causes decolorization, so X reduces KMnO4 and acts as a reducing agent.
• Aqueous KI contains colorless I⁻ ions, oxidized to brown I₂ by oxidizing agents.
• Gas Y causes browning, so Y oxidizes I⁻ and acts as an oxidizing agent.

Why B is correct:

• B matches X reducing KMnO4 (MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H₂O) and Y oxidizing KI (2I⁻ → I₂ + 2e⁻).

Why the others are wrong:

• A: Labels both oxidizing; X reduces, not oxidizes.
• C: Labels X oxidizing; X causes reduction of KMnO4.
• D: Labels both reducing; Y causes oxidation of I⁻.

Final answer: B