When hydrogen sulphide gas is passed through a blue solution of copper sulphate, a black precipitate of copper sulphide is obtained and the sulphuric acid so formed remains in the solution. The reaction is an example of

Options

A. a combination reaction
B. a displacement reaction
C. a decomposition reaction
D. a double decomposition reaction

Explanation

**Step-by-Step Solution:**

1. **Identify the Reactants:**
- The reactants in the reaction are hydrogen sulfide (H₂S) and copper sulfate (CuSO₄).

2. **Write the Chemical Reaction:**
- When hydrogen sulfide gas is passed through a blue solution of copper sulfate, the reaction can be represented as:
\[ \text{H}_2\text{S} + \text{CuSO}_4 \rightarrow \text{CuS} + \text{H}_2\text{SO}_4 \]
- Here, copper sulfide (CuS) is formed as a black precipitate, and sulfuric acid (H₂SO₄) remains in the solution.

3. **Analyze the Reaction:**
- In this reaction, the sulfide ion (S²⁻) from hydrogen sulfide replaces the sulfate ion (SO₄²⁻) from copper sulfate.
- Simultaneously, the copper ion (Cu²⁺) from copper sulfate replaces the hydrogen ions (H⁺) from hydrogen sulfide.

4. **Classify the Reaction:**
- This type of reaction, where both the positive and negative ions exchange places, is known as a **Double Displacement Reaction** (also known as a Double Replacement Reaction).

5. **Conclusion:**
- Therefore, the reaction of hydrogen sulfide with copper sulfate is an example of a Double Displacement Reaction.