Which of the following orders is true regarding the acidic nature of phenols ?

Options

A. Phenol `gt o-` cresol `lto-` nitrophenol
B. Phenol `lt` o-cresol `lt` o-nitrophenol
C. Phenol `gt` o-cresol `gt` o-nitrophenol
D. phenol `lt` o-cresol `gt` o-nitrophenol

Explanation

To determine the correct order regarding the acidic nature of phenols, we will analyze the acidity of three compounds: phenol, ortho-cresol, and ortho-nitrophenol.

### Step-by-Step Solution:

1. **Understanding the Structure of Phenols**:
- Phenols contain a hydroxyl group (-OH) attached to a benzene ring. The presence of the benzene ring allows for resonance stabilization of the phenoxide ion (the conjugate base formed when phenol donates a proton).

2. **Analyzing Phenol**:
- Phenol can lose a proton to form a phenoxide ion. This ion is stabilized by resonance, making phenol more acidic than alcohols, which do not have such stabilization.

3. **Analyzing Ortho-Cresol**:
- Ortho-cresol has a methyl group (-CH3) attached to the benzene ring along with the -OH group. The methyl group is an electron-donating group (due to the +I effect), which increases the electron density on the benzene ring and destabilizes the phenoxide ion. Thus, ortho-cresol is less acidic than phenol.

4. **Analyzing Ortho-Nitrophenol**:
- Ortho-nitrophenol has a nitro group (-NO2) attached to the benzene ring in addition to the -OH group. The nitro group is a strong electron-withdrawing group (due to the -I and -R effects), which stabilizes the phenoxide ion by dispersing the negative charge. Therefore, ortho-nitrophenol is more acidic than both phenol and ortho-cresol.

5. **Comparing Acidity**:
- Based on the above analysis, we can establish the following order of acidity:
- Ortho-nitrophenol > Phenol > Ortho-cresol

6. **Using pKa Values**:
- The pKa values support our conclusion:
- Ortho-nitrophenol: pKa ≈ 7.23
- Phenol: pKa ≈ 9.98
- Ortho-cresol: pKa ≈ 10.23
- Lower pKa values indicate stronger acids, confirming that ortho-nitrophenol is the strongest acid among the three.

### Conclusion:
The correct order regarding the acidic nature of phenols is:
**Ortho-nitrophenol > Phenol > Ortho-cresol**.