Name the gas that can readily decolourise acidified `KMnO_(4)` solution:

Options

A. `CO_(2)`
B. `SO_(2)`
C. `NO_(2)`
D. `P_(2)O_(5)`

Explanation

To solve the question "Name the gas that can readily decolourise acidified KMnO4 solution," we can follow these steps:

### Step 1: Understand the chemical reaction
We need to identify a gas that can react with acidified potassium permanganate (KMnO4) and cause it to lose its color. KMnO4 is purple in color due to the presence of manganese in a high oxidation state.

**Hint:** Look for gases known for their reducing properties.

### Step 2: Identify potential candidates
Common gases that can act as reducing agents include hydrogen sulfide (H2S), sulfur dioxide (SO2), and carbon monoxide (CO). However, we need to find one that specifically reacts with KMnO4.

**Hint:** Recall the properties of sulfur dioxide (SO2) as a reducing agent.

### Step 3: Confirm the reducing agent
Sulfur dioxide (SO2) is known to act as a reducing agent. When it reacts with acidified KMnO4, it reduces the manganese from a +7 oxidation state in KMnO4 to a +2 oxidation state in manganese sulfate (MnSO4).

**Hint:** Consider the oxidation states involved in the reaction.

### Step 4: Write the balanced chemical equation
The balanced equation for the reaction between KMnO4 and SO2 in an acidic medium is:
\[ 2 \text{KMnO}_4 + 5 \text{SO}_2 + 2 \text{H}_2\text{O} \rightarrow 2 \text{MnSO}_4 + \text{KHSO}_4 + \text{H}_2\text{SO}_4 \]

**Hint:** Check if the products formed indicate a color change.

### Step 5: Analyze the color change
Initially, the KMnO4 solution is purple. Upon reaction with SO2, the solution becomes colorless due to the formation of MnSO4, which does not impart color to the solution.

**Hint:** Think about the visual evidence of the reaction.

### Conclusion
The gas that can readily decolourise acidified KMnO4 solution is **sulfur dioxide (SO2)**.

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