Arrange the following compounds in decreasing order of acidity.
(i) `ClCH_(2)CH_(2)CH_(2)COOH`
(ii) `CH_(3)CHClCH_(2)COOH`
(iii) `CH_(3)CH_(2)CHClCOOH`

Options

A. `I gt II gt III`
B. `III gt II gt I`
C. `I gt III gt II`
D. `III gt I gt II`

Answer

To arrange the compounds in decreasing order of acidity, we need to analyze the structure of each compound and the effects of substituents on acidity.

### Step-by-Step Solution:

1. **Identify the Compounds**:
- (i) `ClCH₂CH₂CH₂COOH` (Compound A)
- (ii) `CH₃CHClCH₂COOH` (Compound B)
- (iii) `CH₃CH₂CHClCOOH` (Compound C)

2. **Understand Acidity**:
- Acidity is determined by the ability of a compound to donate protons (H⁺ ions).
- The presence of electron-withdrawing groups (EWGs) increases acidity by stabilizing the negative charge on the conjugate base formed after deprotonation.
- Conversely, electron-donating groups (EDGs) decrease acidity.

3. **Analyze Each Compound**:
- **Compound A**: `ClCH₂CH₂CH₂COOH`
- The Cl group is attached to the first carbon. It has a -I (inductive) effect, but it is relatively far from the carboxylic acid group, which reduces its effectiveness in stabilizing the conjugate base.

- **Compound B**: `CH₃CHClCH₂COOH`
- The Cl group is on the second carbon, closer to the carboxylic acid group. This means it has a stronger -I effect compared to Compound A, thus increasing the acidity more effectively.

- **Compound C**: `CH₃CH₂CHClCOOH`
- The Cl group is on the third carbon. While it still exerts a -I effect, it is further away from the carboxylic acid group than in Compound B, making it less effective in stabilizing the conjugate base compared to Compound B.

4. **Order of Acidity**:
- Based on the analysis, the order of acidity can be determined as follows:
- Compound B (CH₃CHClCH₂COOH) has the highest acidity due to the Cl group being closest to the carboxylic acid group.
- Compound C (CH₃CH₂CHClCOOH) is next, as the Cl group is still an EWG but further away.
- Compound A (ClCH₂CH₂CH₂COOH) has the lowest acidity due to the Cl group being the farthest from the carboxylic acid group.

### Final Order:
The decreasing order of acidity is:
**(ii) > (iii) > (i)** or **B > C > A**.