Pick out the incorrect statement for `SO_2`.

Options

A. It turns filter paper moistened with acidified `K_2Cr_2O_7` solution green
B. It turns starch iodate paper blue
C. It does not react with chlorine in presence of charcoal
D. It decolourieses acidified `KMnO_4` solution

Answer

To solve the problem of identifying the incorrect statement regarding sulfur dioxide (SO₂), we will evaluate each of the provided statements one by one.

### Step-by-Step Solution:

1. **Evaluate the First Statement:**
- **Statement:** SO₂ gas turns filter paper moistened with acidified K₂Cr₂O₇ solution green.
- **Explanation:** When SO₂ is passed through acidified potassium dichromate (K₂Cr₂O₇), it reduces the orange dichromate ion (Cr₂O₇²⁻) to green chromium sulfate (Cr₂(SO₄)₃).
- **Conclusion:** This statement is **correct**.

2. **Evaluate the Second Statement:**
- **Statement:** SO₂ turns starch iodide paper blue.
- **Explanation:** SO₂ acts as a reducing agent and can reduce iodine (I₂) to iodide (I⁻), which can lead to a blue color when starch is present.
- **Conclusion:** This statement is **correct**.

3. **Evaluate the Third Statement:**
- **Statement:** SO₂ does not react with chlorine in the presence of charcoal.
- **Explanation:** SO₂ does react with chlorine in the presence of charcoal to form sulfur dichloride (SO₂Cl₂). Therefore, this statement is incorrect.
- **Conclusion:** This statement is **incorrect**.

4. **Evaluate the Fourth Statement:**
- **Statement:** SO₂ decolorizes acidified KMnO₄ solution.
- **Explanation:** SO₂ can reduce permanganate ions (MnO₄⁻) in an acidified solution to manganese sulfate (MnSO₄), which is colorless, thus decolorizing the purple KMnO₄ solution.
- **Conclusion:** This statement is **correct**.

### Final Answer:
The incorrect statement regarding SO₂ is the **third statement**: "SO₂ does not react with chlorine in the presence of charcoal."

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