Which of the following changes involve reduction ?

Options

A. The conversion of ferrous sulphate to ferric sulphate
B. The conversion of `H_(2)S` to S
C. The conversion of `Cl_(2)` to `NaCl`
D. The conversion of Zn to `ZnSO_(4)`

Answer

To determine which of the given changes involves reduction, we need to analyze the oxidation states of the elements involved in each reaction. Reduction is defined as the gain of electrons or a decrease in oxidation state. Let's evaluate each option step by step.

### Step-by-Step Solution:

1. **Option A: Conversion of Ferrous Sulphate to Ferric Sulphate**
- **Chemical Reaction**: FeSO₄ (ferrous sulphate) → Fe₂(SO₄)₃ (ferric sulphate)
- **Oxidation State**:
- In FeSO₄, the oxidation state of Fe is +2.
- In Fe₂(SO₄)₃, the oxidation state of Fe is +3.
- **Analysis**: The oxidation state of iron increases from +2 to +3, indicating oxidation, not reduction.

2. **Option B: Conversion of Hydrogen Sulphide to Sulphur**
- **Chemical Reaction**: H₂S → S (sulphur)
- **Oxidation State**:
- In H₂S, the oxidation state of S is -2.
- In elemental sulphur (S), the oxidation state is 0.
- **Analysis**: The oxidation state of sulphur increases from -2 to 0, indicating oxidation, not reduction.

3. **Option C: Conversion of Chlorine to Sodium Chloride**
- **Chemical Reaction**: Cl₂ → NaCl
- **Oxidation State**:
- In Cl₂ (elemental chlorine), the oxidation state is 0.
- In NaCl, the oxidation state of Cl is -1.
- **Analysis**: The oxidation state of chlorine decreases from 0 to -1, indicating reduction.

4. **Option D: Conversion of Zinc to Zinc Sulphate**
- **Chemical Reaction**: Zn → ZnSO₄
- **Oxidation State**:
- In elemental zinc (Zn), the oxidation state is 0.
- In zinc sulphate (ZnSO₄), the oxidation state of Zn is +2.
- **Analysis**: The oxidation state of zinc increases from 0 to +2, indicating oxidation, not reduction.

### Conclusion:
The only change that involves reduction is **Option C: Conversion of Chlorine to Sodium Chloride**, where the oxidation state of chlorine decreases from 0 to -1.

### Final Answer:
**C: Conversion of Chlorine to NaCl involves reduction.**

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