Identify the gas that readily decolourises acidified KMnO ₄ solution.

Step-by-step solution

Acidified KMnO ₄ acts as a strong oxidizing agent. SO ₂ is a good reducing agent and readily reduces the purple-coloured acidified KMnO ₄ solution to colourless Mn ²⁺ ions. The chemical reaction is given by: 2 KMnO ₄ + 5 SO ₂ + 2 H ₂ O K ₂ SO ₄ + 2 MnSO ₄ + 2 H ₂ SO ₄ CO ₂ does not react with KMnO ₄ . While H ₂ S can also reduce KMnO ₄ , it produces a milky suspension of colloidal sulphur, whereas SO ₂ yields a clear, colourless solution. Thus, SO ₂ is the gas that readily decolourises the solution. Answer: SO ₂