To determine which compound is less acidic than phenol, we need to analyze the acidity of phenol in comparison to the given options: acetic acid, para-methoxy phenol, para-nitrophenol, and ethanol.
### Step-by-Step Solution:
1. **Understanding Phenol's Acidity**:
- Phenol (C6H5OH) has a hydroxyl group (-OH) attached to a benzene ring. The acidity of phenol is due to the ability of the phenoxide ion (C6H5O-) to stabilize the negative charge through resonance.
2. **Comparing with Acetic Acid (Option A)**:
- Acetic acid (CH3COOH) is a carboxylic acid. Carboxylic acids are generally more acidic than phenols because the carboxylate ion (CH3COO-) formed after deprotonation is stabilized by resonance.
- **Conclusion**: Acetic acid is more acidic than phenol.
3. **Comparing with Para-Methoxy Phenol (Option B)**:
- Para-methoxy phenol (C6H4(OH)(OCH3)) has a methoxy group (-OCH3) which is an electron-donating group. This group increases electron density on the benzene ring and decreases the acidity of the hydroxyl group.
- **Conclusion**: Para-methoxy phenol is less acidic than phenol.
4. **Comparing with Para-Nitrophenol (Option C)**:
- Para-nitrophenol (C6H4(OH)(NO2)) has a nitro group (-NO2) which is an electron-withdrawing group. This group stabilizes the phenoxide ion by pulling electron density away from the ring, thus increasing the acidity.
- **Conclusion**: Para-nitrophenol is more acidic than phenol.
5. **Comparing with Ethanol (Option D)**:
- Ethanol (CH3CH2OH) has a hydroxyl group but lacks the resonance stabilization that phenol has. Therefore, ethanol is less acidic than phenol.
- **Conclusion**: Ethanol is less acidic than phenol.
### Final Conclusion:
Among the options, **para-methoxy phenol and ethanol** are less acidic than phenol. However, if the question is asking for a single answer, **ethanol** is the simplest and most straightforward answer as it is a common alcohol and is less acidic than phenol.
