The correct order of leaving group ability in a nucleophilic substitution reaction is

Options

A. `Br^(-) gt Cl^(-) gt CH_(3)CO_(2)^(-) gt HO^(-) gt H^(-)`
B. `H^(-) gt OH^(-) gt CH_(3)CO_(2)^(-) gt Cl^(-) gt Br^(-)`
C. `Br^(-) gt CH_(3)CO_(2)^(-) gt Cl^(-) gt OH^(-) gt H^(-)`
D. `CH_(3)CO_(2)^(-) gt Br^(-) gt Cl^(-) gt OH^(-) gt H^(-)`

Answer

To determine the correct order of leaving group ability in a nucleophilic substitution reaction, we need to consider the strength of the leaving groups, which is inversely related to their basicity. The weaker the base, the better the leaving group.

### Step-by-Step Solution:

1. **Identify the Leaving Groups**: The leaving groups mentioned are Br⁻, Cl⁻, CH₃COO⁻ (acetate), H₂O, and H₂.

2. **Understand Acid-Base Relationships**: The ability of a leaving group is related to the strength of the corresponding acid. A stronger acid will have a weaker conjugate base, which makes it a better leaving group.

3. **Rank the Acids**:
- HBr (strong acid)
- HCl (strong acid)
- CH₃COOH (weak acid)
- H₂O (weaker acid)
- H₂ (very weak acid)

The order of acidity corresponds to the strength of the conjugate bases:
- Br⁻ (from HBr)
- Cl⁻ (from HCl)
- CH₃COO⁻ (from CH₃COOH)
- H₂O (from H₂O)
- H₂ (from H₂)

4. **Determine the Leaving Group Ability**: The weaker the base, the better the leaving group. Therefore, we can rank the leaving groups based on the strength of their conjugate acids:
- Br⁻ (best leaving group)
- Cl⁻
- CH₃COO⁻
- H₂O
- H₂ (worst leaving group)

5. **Final Order of Leaving Group Ability**: The correct order of leaving group ability from best to worst is:
- Br⁻ > Cl⁻ > CH₃COO⁻ > H₂O > H₂

### Conclusion:
The correct order of leaving group ability in a nucleophilic substitution reaction is Br⁻ > Cl⁻ > CH₃COO⁻ > H₂O > H₂.