Consider the acidity of the carboxylic acids :
`(i) PHCOOH" "(ii) o-NO_(2)C_(6)H_(4)COOH" "(iii) p-NO_(2)C_(6)H_(4)COOH" "(iv) m-NO_(2)C_(6)H_(4)COOH`

Options

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

Answer

To determine the acidity of the given carboxylic acids, we need to analyze the effect of substituents on the acidity of the carboxylic acid group (-COOH). The presence of electron-withdrawing groups (EWGs) increases the acidity of carboxylic acids, and their position relative to the carboxylic acid group plays a crucial role in this effect.

### Step-by-Step Solution:

1. **Identify the Compounds**: We have four carboxylic acids to consider:
- (i) Benzoic acid (PHCOOH)
- (ii) o-Nitrobenzoic acid (o-NO₂C₆H₄COOH)
- (iii) p-Nitrobenzoic acid (p-NO₂C₆H₄COOH)
- (iv) m-Nitrobenzoic acid (m-NO₂C₆H₄COOH)

2. **Understand the Effect of Substituents**:
- Electron-withdrawing groups (like -NO₂) increase acidity by stabilizing the negative charge on the carboxylate ion formed after deprotonation.
- The ortho position (o-) has a stronger effect than the para position (p-), and the meta position (m-) has the least effect.

3. **Rank the Acidity**:
- **o-NO₂C₆H₄COOH**: The nitro group is at the ortho position, which has the strongest electron-withdrawing effect, thus making this compound the most acidic.
- **p-NO₂C₆H₄COOH**: The nitro group is at the para position, which has a strong electron-withdrawing effect but is less effective than the ortho position.
- **m-NO₂C₆H₄COOH**: The nitro group is at the meta position, which has a weaker electron-withdrawing effect compared to ortho and para positions.
- **PHCOOH**: Benzoic acid has no electron-withdrawing group and will be the least acidic among the four.

4. **Final Order of Acidity**: Based on the above analysis, the order of acidity from strongest to weakest is:
- (ii) o-NO₂C₆H₄COOH > (iii) p-NO₂C₆H₄COOH > (iv) m-NO₂C₆H₄COOH > (i) PHCOOH

### Conclusion:
The correct order of acidity for the given carboxylic acids is:
**o-NO₂C₆H₄COOH > p-NO₂C₆H₄COOH > m-NO₂C₆H₄COOH > PHCOOH**