What happens when:
`SO_2` gas is passed through `KMnO_4` solution.

Answer

When sulfur dioxide gas (`SO₂`) is passed through a potassium permanganate (`KMnO₄`) solution, a chemical reaction occurs that results in the formation of several products. Here’s a step-by-step breakdown of the process:

### Step 1: Understanding the Reactants
- **Sulfur Dioxide (`SO₂`)**: This is a colorless gas with a pungent smell, commonly produced by the burning of fossil fuels.
- **Potassium Permanganate (`KMnO₄`)**: This is a strong oxidizing agent, typically purple in color due to the presence of manganese in a +7 oxidation state.

### Step 2: The Reaction
When `SO₂` is introduced into the `KMnO₄` solution, it acts as a reducing agent. The `SO₂` reduces the manganese from the +7 oxidation state in `KMnO₄` to a +2 oxidation state in manganese sulfate (`MnSO₄`), while itself being oxidized to sulfate ions.

### Step 3: Products Formed
The products of the reaction are:
1. **Potassium Sulfate (`K₂SO₄`)**: Formed from the potassium ions in the `KMnO₄` and the sulfate ions produced from the oxidation of `SO₂`.
2. **Manganese Sulfate (`MnSO₄`)**: Formed from the reduction of `KMnO₄`.
3. **Sulfuric Acid (`H₂SO₄`)**: Also formed as a product of the oxidation of `SO₂`.

### Step 4: Color Change
- The initial purple color of the `KMnO₄` solution will disappear (decolorize) as the reaction proceeds. This is because the manganese is reduced from the +7 state (purple) to the +2 state (colorless).

### Final Reaction Equation
The overall reaction can be summarized as:
\[ 5SO_2 + 2KMnO_4 + 2H_2O \rightarrow K_2SO_4 + 2MnSO_4 + H_2SO_4 \]

### Conclusion
In conclusion, when `SO₂` gas is passed through `KMnO₄` solution, it results in the formation of potassium sulfate, manganese sulfate, and sulfuric acid, while the purple color of the `KMnO₄` solution disappears.

---