The decreasing leaving group order of the following is:
i. `F_(3)CSO_(3)^(o-)`, ii. `Cl_(3)C-COO^(o-)`
iii. `PhSO_(3)^(o-)`, iv. `MeSO_(3)^(o-)`

Options

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

Explanation

To determine the decreasing leaving group order of the given species:

1. **Identify the Species**: We have four species to analyze:
- i. `F_(3)CSO_(3)^(o-)` (CF3SO3^-)
- ii. `Cl_(3)C-COO^(o-)` (Cl3C-COO^-)
- iii. `PhSO_(3)^(o-)` (PhSO3^-)
- iv. `MeSO_(3)^(o-)` (MeSO3^-)

2. **Understand Leaving Groups and Basicity**: The strength of a leaving group is inversely related to the basicity of the corresponding conjugate base. Strong bases are poor leaving groups, while weak bases are good leaving groups.

3. **Find Conjugate Acids**: To analyze the basicity, we need to find the conjugate acids of the given species by adding H+:
- For `CF3SO3^-`, the conjugate acid is `CF3SO3H`.
- For `Cl3C-COO^-`, the conjugate acid is `Cl3C-COOH`.
- For `PhSO3^-`, the conjugate acid is `PhSO3H`.
- For `MeSO3^-`, the conjugate acid is `MeSO3H`.

4. **Compare Acidic Strength**: The acidic strength of these conjugate acids will help us determine the basicity:
- Sulfonic acids (like CF3SO3H, PhSO3H, MeSO3H) are generally stronger than carboxylic acids (like Cl3C-COOH).
- Among the sulfonic acids, `CF3SO3H` is the strongest due to the strong electron-withdrawing effect of the CF3 group.
- Next, `PhSO3H` is stronger than `MeSO3H` because the phenyl group has a -I (inductive) effect, making it more acidic than the electron-donating methyl group.

5. **Order of Acidic Strength**: Based on the above analysis, the order of acidic strength is:
- 1. `CF3SO3H` (strongest)
- 2. `PhSO3H`
- 3. `MeSO3H`
- 4. `Cl3C-COOH` (weakest)

6. **Determine Basic Strength**: The basic strength order is the reverse of the acidic strength:
- 1. `Cl3C-COO^-` (weakest base)
- 2. `MeSO3^-`
- 3. `PhSO3^-`
- 4. `CF3SO3^-` (strongest base)

7. **Determine Leaving Group Order**: The leaving group order is the reverse of the basic strength:
- 1. `CF3SO3^-` (best leaving group)
- 2. `PhSO3^-`
- 3. `MeSO3^-`
- 4. `Cl3C-COO^-` (poorest leaving group)

Thus, the final decreasing order of leaving groups is:
- `CF3SO3^- > PhSO3^- > MeSO3^- > Cl3C-COO^-`

### Final Answer:
The decreasing leaving group order is:
1. `CF3SO3^-`
2. `PhSO3^-`
3. `MeSO3^-`
4. `Cl3C-COO^-`