Write a chemical reaction to test sulphur dioxide gas. Write chemical equation involved.

Explanation

To test for sulfur dioxide (SO₂) gas, we can use potassium dichromate (K₂Cr₂O₇) in the presence of sulfuric acid (H₂SO₄). The reaction involves the oxidation of sulfur dioxide and the reduction of potassium dichromate.

### Step-by-Step Solution:

1. **Identify the Reactants**: The reactants for this reaction are sulfur dioxide (SO₂), potassium dichromate (K₂Cr₂O₇), and sulfuric acid (H₂SO₄).

2. **Write the Reaction**: When sulfur dioxide is passed through an acidified solution of potassium dichromate, it oxidizes the sulfur dioxide to sulfuric acid while reducing the dichromate ion to chromium(III) sulfate.

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