Which of the following is a weaker acid than phenol?

Options

A. 4-Methoxy phenol
B. 3, 5-dinitrophenol
C. 4-Methyl phenol
D. 4-Nitrophenol

Answer

To determine which of the given acids is weaker than phenol, we need to analyze the acidity of the compounds mentioned in the question. The acidity of a compound is influenced by the stability of its conjugate base after it donates a proton (H⁺).

### Step-by-Step Solution:

1. **Understanding Phenol's Structure**:
- Phenol has the structure C₆H₅OH, where the hydroxyl group (-OH) is directly attached to a benzene ring. The acidity of phenol is due to its ability to donate a proton to form the phenoxide ion (C₆H₅O⁻).

2. **Analyzing the Conjugate Base**:
- When phenol loses a proton, it forms the phenoxide ion, which is stabilized by resonance. This resonance allows the negative charge to be delocalized over the aromatic ring, increasing the stability of the ion.

3. **Comparing with Other Compounds**:
- **3,5-Dinitrophenol**: This compound has two nitro groups which are strong electron-withdrawing groups. They stabilize the conjugate base (phenoxide ion) by resonance and inductive effects, making it a stronger acid than phenol.
- **4-Nitrophenol**: Similar to 3,5-Dinitrophenol, the nitro group in this compound also acts as an electron-withdrawing group, stabilizing the conjugate base and making it a stronger acid than phenol.
- **4-Methoxyphenol**: The methoxy group (-OCH₃) is an electron-donating group due to its +R (resonance) effect. This increases the electron density on the aromatic ring and destabilizes the conjugate base (phenoxide ion), making 4-Methoxyphenol a weaker acid than phenol.

4. **Conclusion**:
- Among the compounds analyzed, **4-Methoxyphenol** is the only one that is a weaker acid than phenol due to the electron-donating effect of the methoxy group, which destabilizes the phenoxide ion.

### Final Answer:
**4-Methoxyphenol is a weaker acid than phenol.**