The strongest acid among the following aromatic compound is:

Options

A. o-Nitrophenol
B. p-Chlorophenol
C. p-Nitrophenol
D. m-Nitrophenol

Explanation

To determine the strongest acid among the given aromatic compounds, we will analyze the effects of substituents on their acidity.

### Step-by-Step Solution:

1. **Identify the Compounds**:
We need to consider the aromatic compounds given in the question. Let's assume we have nitrophenol and chlorophenol as the main candidates.

2. **Understand Electron-Withdrawing Groups**:
Both the nitro group (-NO2) and the chlorine atom (-Cl) are electron-withdrawing groups. Electron-withdrawing groups increase the acidity of aromatic compounds by stabilizing the negative charge on the conjugate base formed after deprotonation.

3. **Compare the Effects of Substituents**:
- **Nitrophenol**: The nitro group is a strong electron-withdrawing group due to its resonance and inductive effects. It can stabilize the negative charge on the phenoxide ion (the conjugate base) formed when nitrophenol loses a proton.
- **Chlorophenol**: The chlorine atom is also an electron-withdrawing group, but it is less effective than the nitro group in stabilizing the negative charge due to its weaker resonance effect.

4. **Consider Resonance Effects**:
- In nitrophenol, the nitro group can participate in resonance at the ortho and para positions, which helps stabilize the conjugate base.
- In chlorophenol, the chlorine can also participate in resonance, but its effect is weaker than that of the nitro group.

5. **Analyze Ortho and Para Positions**:
- **Ortho-Nitrophenol**: While it can stabilize the conjugate base through resonance, it can also form intramolecular hydrogen bonding, which reduces its acidity.
- **Para-Nitrophenol**: This compound does not have the intramolecular hydrogen bonding issue and can effectively stabilize the conjugate base through resonance.

6. **Conclusion**:
Since para-nitrophenol has the strongest electron-withdrawing effect and does not suffer from the intramolecular hydrogen bonding that affects ortho-nitrophenol, it is the strongest acid among the compounds considered.

### Final Answer:
The strongest acid among the given aromatic compounds is **para-nitrophenol**.

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