Consider the acidity of the carboxylic acids:
(1) `PhCOOH`
(2) `o-NO_(2) C_(6) H_(4) COOH`
(3) `p-NO_(2) C_(6) H_(4) COOH`
(4) `m-NO_(2) C_(6) H_(4) COOH`
Which of the following order is correct?

Options

A. igtiigtiiigtiv
B. iigtivgtiiigti
C. iigtivgtigtiii
D. iigtiiigtivgti

Answer

To determine the correct order of acidity for the given carboxylic acids, we will analyze the compounds step by step based on the effects of substituents on the acidity of benzoic acid derivatives.

### Step 1: Identify the Compounds
We have the following compounds:
1. `PhCOOH` (Benzoic acid)
2. `o-NO2C6H4COOH` (Ortho-nitrobenzoic acid)
3. `p-NO2C6H4COOH` (Para-nitrobenzoic acid)
4. `m-NO2C6H4COOH` (Meta-nitrobenzoic acid)

### Step 2: Understand the Effects of the Nitro Group
The nitro group (`-NO2`) is an electron-withdrawing group. It increases the acidity of carboxylic acids because it stabilizes the negative charge on the carboxylate ion formed after deprotonation.

### Step 3: Analyze the Position of the Nitro Group
- **Ortho Position (`o-NO2`)**: The ortho effect enhances acidity due to steric and electronic factors. The nitro group at the ortho position can stabilize the carboxylate ion effectively, making ortho-nitrobenzoic acid the most acidic.
- **Para Position (`p-NO2`)**: The para position also allows for effective stabilization of the carboxylate ion due to the electron-withdrawing effect of the nitro group. However, it is less effective than the ortho position.
- **Meta Position (`m-NO2`)**: The nitro group at the meta position does not have the same resonance effect as in the ortho and para positions. It primarily exerts a -I (inductive) effect but lacks the -M (mesomeric) effect, making it less acidic than both ortho and para derivatives.

### Step 4: Compare the Acidity
Based on the above analysis, we can summarize the acidity order:
1. **Ortho-nitrobenzoic acid (`o-NO2C6H4COOH`)** - Most acidic due to ortho effect.
2. **Para-nitrobenzoic acid (`p-NO2C6H4COOH`)** - Less acidic than ortho but more acidic than meta and benzoic acid.
3. **Meta-nitrobenzoic acid (`m-NO2C6H4COOH`)** - Less acidic than both ortho and para due to lack of resonance stabilization.
4. **Benzoic acid (`PhCOOH`)** - Least acidic as it has no electron-withdrawing group.

### Final Order of Acidity
The correct order of acidity is:
`o-NO2C6H4COOH > p-NO2C6H4COOH > m-NO2C6H4COOH > PhCOOH`

### Conclusion
Thus, the correct answer is:
**Option D: o-NO2C6H4COOH > p-NO2C6H4COOH > m-NO2C6H4COOH > PhCOOH**

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