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. 2 `gt` 3 `gt` 4 `gt` 1
B. 2 `gt` 4 `gt` 3 `gt` 1
C. 2 `gt` 4 `gt` 1 `gt` 3
D. 1 `gt` 2 `gt` 3 `gt` 4

Explanation

To determine the correct order of acidity among the given carboxylic acids, we will analyze the stability of their conjugate bases. The stability of the conjugate base is influenced by the presence of electron-withdrawing groups, which can stabilize the negative charge that results when the acid donates a proton.

### Step-by-Step Solution:

1. **Identify the Compounds**:
- (1) PhCOOH (Benzoic acid)
- (2) o-NO2C6H4COOH (Ortho-nitrobenzoic acid)
- (3) p-NO2C6H4COOH (Para-nitrobenzoic acid)
- (4) m-NO2C6H4COOH (Meta-nitrobenzoic acid)

2. **Understand Acidity**:
- Acidity is related to the stability of the conjugate base. The more stable the conjugate base, the stronger the acid.

3. **Analyze Benzoic Acid (PhCOOH)**:
- Benzoic acid does not have any electron-withdrawing groups, making it the weakest acid among the four.

4. **Analyze Ortho-Nitrobenzoic Acid (o-NO2C6H4COOH)**:
- The nitro group is positioned ortho to the carboxylic acid group. This position allows for strong resonance and inductive effects, significantly stabilizing the conjugate base. Thus, it is the strongest acid.

5. **Analyze Para-Nitrobenzoic Acid (p-NO2C6H4COOH)**:
- The nitro group is in the para position. It also stabilizes the conjugate base through resonance and inductive effects, but not as effectively as the ortho position. Therefore, it is the second strongest acid.

6. **Analyze Meta-Nitrobenzoic Acid (m-NO2C6H4COOH)**:
- The nitro group in the meta position has a weaker effect on the carboxylic acid group compared to the ortho and para positions. Thus, it is the weakest among the nitro-substituted acids.

7. **Establish the Order of Acidity**:
- From strongest to weakest:
- (2) o-NO2C6H4COOH > (3) p-NO2C6H4COOH > (4) m-NO2C6H4COOH > (1) PhCOOH
- Therefore, the correct order of acidity is 2341.

### Final Answer:
The correct order of acidity is: **o-NO2C6H4COOH > p-NO2C6H4COOH > m-NO2C6H4COOH > PhCOOH** (2341).