Acidified `KMnO_(4)` can be decolourised by (a)_____.

Answer

To solve the question "Acidified KMnO₄ can be decolourised by (a)_____", we need to identify substances that can reduce potassium permanganate (KMnO₄) in an acidic medium, leading to its decolouration.

### Step-by-Step Solution:

1. **Understanding KMnO₄**:
- Potassium permanganate (KMnO₄) is a strong oxidizing agent, particularly in acidic solutions. It has a deep purple color due to the presence of MnO₄⁻ ions.

2. **Identifying Reducing Agents**:
- To decolourize KMnO₄, we need to find substances that can act as reducing agents. Common reducing agents include:
- Ferrous ions (Fe²⁺)
- Oxalate ions (C₂O₄²⁻)
- Sulfur dioxide (SO₂)

3. **Reactions Involved**:
- **Ferrous ions (Fe²⁺)**:
- The reaction can be represented as:
\[ \text{MnO}_4^- + 5\text{Fe}^{2+} + 8\text{H}^+ \rightarrow 2\text{Mn}^{2+} + 5\text{Fe}^{3+} + 4\text{H}_2\text{O} \]
- Here, Fe²⁺ oxidizes to Fe³⁺ while MnO₄⁻ reduces to Mn²⁺, resulting in decolouration.

- **Oxalate ions (C₂O₄²⁻)**:
- The reaction can be represented as:
\[ 2\text{MnO}_4^- + 5\text{C}_2\text{O}_4^{2-} + 16\text{H}^+ \rightarrow 2\text{Mn}^{2+} + 10\text{CO}_2 + 8\text{H}_2\text{O} \]
- In this case, oxalate ions are oxidized to carbon dioxide while MnO₄⁻ is reduced to Mn²⁺.

- **Sulfur dioxide (SO₂)**:
- The reaction can be represented as:
\[ 2\text{MnO}_4^- + 5\text{SO}_2 + 8\text{H}^+ \rightarrow 2\text{Mn}^{2+} + 5\text{H}_2\text{SO}_4 \]
- Here, SO₂ reduces MnO₄⁻ to Mn²⁺, leading to decolouration.

4. **Final Answer**:
- Therefore, acidified KMnO₄ can be decolourized by **Fe²⁺, C₂O₄²⁻, or SO₂**.

### Fill in the Blank:
Acidified KMnO₄ can be decolourised by (a) **Fe²⁺, C₂O₄²⁻, or SO₂**.