Which one of the following is the correct order of acidic strength?
(i) `Cl_(3)C-COOH`
(ii) `Cl_(2)CH-COOH`
(iii) `ClCH_(2)-COOH`
(iv) `CH_(3)-COOH`

Options

A. `iv gt iii gt ii gt i`
B. `igt ii gt iii gt iv`
C. `igt iii gt ii gt iv`
D. `iv gt ii gt iii gt i`

Answer

To determine the correct order of acidic strength among the given compounds, we need to analyze how the substituents attached to the carboxylic acid group affect the stability of the conjugate base formed after deprotonation. The more stable the conjugate base, the stronger the acid.

### Step-by-Step Solution:

1. **Identify the Compounds**:
- (i) `Cl3C-COOH` (Trichloroacetic acid)
- (ii) `Cl2CH-COOH` (Dichloroacetic acid)
- (iii) `ClCH2-COOH` (Monochloroacetic acid)
- (iv) `CH3-COOH` (Acetic acid)

2. **Understand the Effect of Substituents**:
- Chlorine (Cl) is an electron-withdrawing group (EWG) due to its electronegativity. The more chlorine atoms present, the stronger the electron-withdrawing effect.
- Electron-withdrawing groups stabilize the negative charge on the conjugate base, making the acid stronger.

3. **Analyze Each Compound**:
- **(i) `Cl3C-COOH`**: The presence of three chlorine atoms leads to a strong -I (inductive) effect, significantly stabilizing the conjugate base.
- **(ii) `Cl2CH-COOH`**: With two chlorine atoms, this compound also has a strong -I effect, but it is less than that of (i).
- **(iii) `ClCH2-COOH`**: This compound has only one chlorine atom, providing a weaker -I effect compared to the previous two.
- **(iv) `CH3-COOH`**: The methyl group (CH3) is an electron-donating group (+I effect), which destabilizes the conjugate base, making it the weakest acid among the four.

4. **Order of Acidity**:
- Based on the analysis, the order of acidic strength from strongest to weakest is:
- (i) `Cl3C-COOH` > (ii) `Cl2CH-COOH` > (iii) `ClCH2-COOH` > (iv) `CH3-COOH`

### Final Answer:
The correct order of acidic strength is:
**(i) > (ii) > (iii) > (iv)**