Arrange the following in order of decreasing acidic strength. p-nitrophenol (I), m-cresol (II),phenol(III):

Options

A. `IgtIIIgtII`
B. `IIIgtIIgtI`
C. `IgtIIIgtII`
D. `IIIgtIIgtI
`

Answer

To arrange the compounds p-nitrophenol (I), m-cresol (II), and phenol (III) in order of decreasing acidic strength, we need to analyze the effects of the substituents on the phenolic compounds.

### Step-by-Step Solution:

1. **Identify the Compounds**:
- p-Nitrophenol (I): Contains a nitro group (-NO2) at the para position relative to the hydroxyl group (-OH).
- m-Cresol (II): Contains a methyl group (-CH3) at the meta position relative to the hydroxyl group.
- Phenol (III): Contains only the hydroxyl group attached to the benzene ring.

2. **Understand the Effects of Substituents**:
- The nitro group in p-nitrophenol is a strong electron-withdrawing group due to its -I (inductive) and -R (resonance) effects. This increases the acidity by stabilizing the phenoxide ion formed after deprotonation.
- The methyl group in m-cresol is an electron-donating group due to its +I (inductive) effect. This increases the electron density around the ring and destabilizes the phenoxide ion, thus decreasing acidity.
- Phenol itself has no additional substituents that significantly affect its acidity.

3. **Compare Acidity**:
- **p-Nitrophenol (I)**: The strong electron-withdrawing effect of the nitro group makes p-nitrophenol the most acidic among the three.
- **Phenol (III)**: The acidity of phenol is greater than that of m-cresol but less than that of p-nitrophenol.
- **m-Cresol (II)**: The presence of the methyl group decreases the acidity compared to phenol due to its electron-donating effect.

4. **Order of Acidity**:
- Based on the analysis, we can arrange the compounds in order of decreasing acidic strength:
- **p-Nitrophenol (I) > Phenol (III) > m-Cresol (II)**.

### Final Answer:
**p-Nitrophenol (I) > Phenol (III) > m-Cresol (II)**