When copper metal is treated with concentrated sulphuric acid, the gas liberated is 

Options

A. Hydrogen
B. Sulphur dioxide
C. Hydrogen sulphide
D. Ammonia

Answer

To determine the gas liberated when copper metal is treated with concentrated sulfuric acid, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Reactants**:
- The reactants in this reaction are copper metal (Cu) and concentrated sulfuric acid (H₂SO₄).

2. **Write the Chemical Reaction**:
- When copper reacts with concentrated sulfuric acid, the products formed are copper sulfate (CuSO₄), sulfur dioxide (SO₂), and water (H₂O).
- The balanced chemical equation for this reaction is:
\[ Cu + 2H_2SO_4 \rightarrow CuSO_4 + SO_2 + 2H_2O \]

3. **Identify the Gas Liberated**:
- From the balanced equation, we can see that sulfur dioxide (SO₂) is the gas that is liberated during this reaction.

4. **Confirm the Gas**:
- To confirm that the gas produced is sulfur dioxide, we can perform a simple test. If we pass the gas through an acidified potassium dichromate (K₂Cr₂O₇) solution, which is orange in color, it will change color to green. This color change indicates the presence of sulfur dioxide due to the reduction of chromium from +6 to +3 oxidation state.

5. **Conclusion**:
- Therefore, the gas liberated when copper metal is treated with concentrated sulfuric acid is sulfur dioxide (SO₂).