Among the following four compounds
(a) Phenol
(b) methyl phenol
(c) metanitrophenol
(d) paranitrophenol
the acidity order is –

Options

A. `c gt d gt a gt b`
B. `a gt d gt c gt b `
C. `b gt a gt c gt d `
D. `d gt c gt a gt b`

Answer

To determine the order of acidity among the given compounds (Phenol, Methyl Phenol, Meta-Nitrophenol, Para-Nitrophenol), we will analyze the effects of substituents on the acidity of phenol.

### Step-by-Step Solution:

1. **Identify the Structures**:
- **Phenol (A)**: C6H5OH
- **Methyl Phenol (B)**: C6H4(CH3)OH (with CH3 at ortho position)
- **Meta-Nitrophenol (C)**: C6H4(NO2)OH (with NO2 at meta position)
- **Para-Nitrophenol (D)**: C6H4(NO2)OH (with NO2 at para position)

2. **Understand Acidity**:
- Acidity is influenced by the stability of the conjugate base formed after deprotonation.
- Electron-withdrawing groups (EWGs) increase acidity by stabilizing the negative charge on the conjugate base, while electron-donating groups (EDGs) decrease acidity.

3. **Analyze Each Compound**:
- **Phenol (A)**: No substituents to affect acidity significantly.
- **Methyl Phenol (B)**: The methyl group (CH3) is an electron-donating group (+I effect), which decreases acidity compared to phenol.
- **Meta-Nitrophenol (C)**: The nitro group (NO2) is an electron-withdrawing group (-I effect) but has no resonance effect at the meta position, thus it only slightly increases acidity.
- **Para-Nitrophenol (D)**: The nitro group (-I and -M effects) stabilizes the conjugate base significantly, leading to increased acidity.

4. **Determine the Order of Acidity**:
- **Para-Nitrophenol (D)** has the highest acidity due to both -I and -M effects.
- **Meta-Nitrophenol (C)** is next, as it has a -I effect but no resonance stabilization.
- **Phenol (A)** follows, as it has no significant electron-donating or withdrawing effects.
- **Methyl Phenol (B)** has the lowest acidity due to the +I effect of the methyl group.

5. **Final Order**:
- The order of acidity from highest to lowest is: **Para-Nitrophenol (D) > Meta-Nitrophenol (C) > Phenol (A) > Methyl Phenol (B)**.

### Conclusion:
The correct order of acidity is: **D > C > A > B**.