Question

Name the gas that can readily decolourises acidified KMnO₄ solution:

• A. CO₂
• B. SO₂
• C. NO₂
• D. P₂O₅

Answer 1

The Correct Option is B

To determine the gas that can readily decolourize an acidified KMnO₄ solution, we need to understand the chemical behavior of the gases with respect to the strong oxidizing nature of KMnO₄.

Concept Explanation: Acidified potassium permanganate (KMnO₄) acts as a strong oxidizing agent. It is often used to test the presence of reducing agents. When a reducing agent is present, KMnO₄ is reduced, causing its purple color to fade.

Gas Analysis:

• CO₂: Carbon dioxide is not a reducing agent and will not react with KMnO₄ to cause decolourization.
• SO₂: Sulphur dioxide is a known reducing agent. It can react with KMnO₄, reducing it from Mn⁷⁺ to Mn²⁺, and change the color from purple to colorless.
• NO₂: Nitrogen dioxide does not have a significant reducing effect on separate conditions with KMnO₄.
• P₂O₅: Phosphorus pentoxide is not a reducing agent and does not react with KMnO₄.

Conclusion: Among the options provided, SO₂ (Sulphur dioxide) is the gas that can readily decolourize acidified KMnO₄ solution. This is due to SO₂ acting as a reducing agent, enabling the reduction of MnO₄^- ions to Mn²⁺, leading to a color change from purple to colorless.