Phenol, `p-`methylphenol, `m-`nitrophenol and `p-`nitrophenol follow order of increasing acidic strength

Options

A. Phenol, `p-` methylphenol, `p-` nitrophenol, `m-` nitrophenol
B. `p-` Methylphenol, phenol, `m-` nitrophenol, `p-` nitrophenol
C. `p-` Methylphenol, `m-` nitrophenol, phenol, `p-` nitrophenol
D. `m-` Nitrophenol, `p-`nitrophenol, and `p-` methylphenol

Explanation

To determine the order of increasing acidic strength among phenol, p-methylphenol, m-nitrophenol, and p-nitrophenol, we need to analyze the effects of the substituents on the phenolic compound.

### Step-by-Step Solution:

1. **Identify the Compounds**:
- We have four compounds:
- Phenol (C6H5OH)
- p-Methylphenol (C6H4(CH3)OH)
- m-Nitrophenol (C6H4(NO2)OH)
- p-Nitrophenol (C6H4(NO2)OH)

2. **Understand the Effects of Substituents**:
- **Electron-Withdrawing Groups (EWGs)**: These groups, such as -NO2, increase the acidity of phenolic compounds by stabilizing the negative charge on the phenoxide ion (the conjugate base).
- **Electron-Donating Groups (EDGs)**: Groups like -CH3 decrease the acidity by destabilizing the negative charge on the phenoxide ion.

3. **Analyze Each Compound**:
- **Phenol**: No substituents, moderate acidity.
- **p-Methylphenol**: The methyl group is an EDG, which decreases acidity compared to phenol.
- **m-Nitrophenol**: The nitro group is an EWG but is in the meta position, which means it only exerts an inductive effect (-I) and does not stabilize the negative charge as effectively as in the para position.
- **p-Nitrophenol**: The nitro group is in the para position, exerting both -I and -R effects, which significantly increases acidity by stabilizing the phenoxide ion.

4. **Rank the Acidity**:
- p-Nitrophenol (strongest acid due to both -I and -R effects)
- m-Nitrophenol (weaker than p-nitrophenol due to only -I effect)
- Phenol (moderate acidity)
- p-Methylphenol (weakest acid due to -CH3 donating electrons)

5. **Final Order of Increasing Acidic Strength**:
- p-Methylphenol < Phenol < m-Nitrophenol < p-Nitrophenol

### Conclusion:
The order of increasing acidic strength is:
**p-Methylphenol < Phenol < m-Nitrophenol < p-Nitrophenol**