The order of leaving group ability is :

Options

A. `(i) gt (ii) gt (iii) gt (iv)`
B. `(iv) gt (iii) gt (i) gt (ii)`
C. `(iii) gt (ii) gt (i) gt (iv)`
D. `(ii) gt (iii) gt (iv) gt (i)`

Explanation

To determine the order of leaving group ability, we need to analyze the stability of the conjugate bases formed when these leaving groups depart. A good leaving group is typically a weak base, as weak bases are more stable and less likely to re-attack the substrate.

### Step-by-Step Solution:

1. **Identify the Leaving Groups**:
Let's denote the leaving groups as A, B, C, and D. We will analyze their conjugate bases after they leave.

2. **Analyze Conjugate Bases**:
- For each leaving group, write down the corresponding conjugate base formed after the leaving group departs.
- Evaluate the stability of each conjugate base. The more stable the conjugate base, the better the leaving group.

3. **Stability Factors**:
- **Resonance**: If the conjugate base can stabilize the negative charge through resonance, it will be more stable.
- **Electronegativity**: More electronegative atoms can stabilize negative charges better.
- **Inductive Effect**: Groups that exhibit a -I effect can also stabilize the negative charge.

4. **Order of Basicity**:
- Based on the stability of the conjugate bases, we can rank them from most basic to least basic.
- The order of basicity will help us determine the order of leaving group ability (the weaker the base, the better the leaving group).

5. **Conclusion**:
- After analyzing the conjugate bases, we find that the order of leaving group ability is the reverse of the order of basicity.
- If the order of basicity is B > A > C > D, then the order of leaving group ability will be D > C > A > B.

### Final Order of Leaving Group Ability:
- D is the best leaving group, followed by C, A, and B as the poorest leaving group.