Question

Identify the gas that readily decolourises acidified \(\text{KMnO}_{4}\) solution.

• A. \(\text{CO}_{2}\)
• B. \(\text{SO}_{2}\)
• C. \(\text{NO}_{2}\)
• D. \(\text{H}_{2}\text{S}\)

Hint:

Acidified permanganate is decolourised by a reducing gas, and sulphur dioxide is the standard example.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept
Acidified \(\text{KMnO}_{4}\) is purple because of \(\text{MnO}_{4}^{-}\). A reducing agent converts it to the almost colourless \(\text{Mn}^{2+}\).

Step 2: Check the gases
\(\text{CO}_{2}\) is already in its highest oxidation state, so it cannot reduce permanganate.
\(\text{NO}_{2}\) is not a typical reducing gas here.
\(\text{SO}_{2}\) is a strong reducing agent and is oxidised to sulphate.

Step 3: Conclusion
\(\text{SO}_{2}\) turns the purple solution colourless, which is the standard test for this gas.

Final Answer:
The gas is \(\text{SO}_{2}\). \[ \boxed{\text{(B) }\text{SO}_{2}} \]