Order of acidic strength of the following compound will be
A) Phenol B) p-Cresol C) m-Nitrophenol D) p-Nitrophenol is :
(a)`CgtDgtBgtA`
(b)`DgtCgtBgtA`
(c)`AgtBgtCgtD`
(d)`BgtAgtCgtD`

Options

A. `CgtDgtBgtA`
B. `DgtCgtBgtA`
C. `AgtBgtCgtD`
D. `BgtAgtCgtD`

Answer

To determine the order of acidic strength of the given compounds (Phenol, p-Cresol, m-Nitrophenol, and p-Nitrophenol), we need to analyze the stability of their conjugate bases. The more stable the conjugate base, the stronger the acid.

### Step-by-Step Solution:

1. **Identify the Compounds and Their Structures**:
- **A) Phenol**: C6H5OH
- **B) p-Cresol**: C6H4(CH3)OH (methyl group at the para position)
- **C) m-Nitrophenol**: C6H4(NO2)OH (nitro group at the meta position)
- **D) p-Nitrophenol**: C6H4(NO2)OH (nitro group at the para position)

2. **Understand Acidic Strength**:
- The acidic strength of a compound is determined by the stability of its conjugate base. A more stable conjugate base corresponds to a stronger acid.

3. **Analyze the Conjugate Bases**:
- **Phenol (A)**: The conjugate base is the phenoxide ion (C6H5O⁻). The negative charge is delocalized over the aromatic ring but is not significantly stabilized.
- **p-Cresol (B)**: The conjugate base is the p-cresoxide ion (C6H4(CH3)O⁻). The methyl group provides a +I (inductive) effect, increasing electron density on the oxygen, making it less stable compared to phenoxide.
- **m-Nitrophenol (C)**: The conjugate base is the m-nitrophenoxide ion (C6H4(NO2)O⁻). The nitro group provides a -I (inductive) effect, stabilizing the conjugate base by withdrawing electron density.
- **p-Nitrophenol (D)**: The conjugate base is the p-nitrophenoxide ion (C6H4(NO2)O⁻). The nitro group here can exert both -I and -M (mesomeric) effects, providing even greater stabilization to the conjugate base.

4. **Rank the Acids Based on Conjugate Base Stability**:
- **D (p-Nitrophenol)**: Most stable conjugate base due to strong -I and -M effects.
- **C (m-Nitrophenol)**: Less stable than D but more stable than A and B due to -I effect.
- **A (Phenol)**: Moderate stability of the conjugate base.
- **B (p-Cresol)**: Least stable conjugate base due to +I effect from the methyl group.

5. **Final Order of Acidity**:
- The order of acidic strength from strongest to weakest is:
**D > C > A > B**.

### Conclusion:
The correct answer is (b) `D > C > B > A`.