Which one is the most acidic compound?

Options

A.
B.
C.
D.

Explanation

To determine which of the given compounds is the most acidic, we will analyze the effects of the substituents attached to the phenol group in each compound.

### Step-by-Step Solution:

1. **Identify the Compounds**:
We have four compounds, all of which are derivatives of phenol. The substituents attached to the phenol group will influence its acidity.

2. **Understand the Effects of Substituents**:
- **Electron-Donating Groups (EDGs)**: Groups that exhibit a +I (inductive) or +R (resonance) effect increase electron density on the phenol ring. This makes it harder for the phenol to lose a proton (H⁺), thus decreasing acidity.
- **Electron-Withdrawing Groups (EWGs)**: Groups that exhibit a -I or -R effect withdraw electron density from the phenol ring. This increases the tendency of the phenol to lose a proton, thus increasing acidity.

3. **Analyze Each Compound**:
- **Compound 1**: Contains a CH₃ group (methyl group), which is an electron-donating group (+I effect). This will decrease the acidity of phenol.
- **Compound 2**: Contains no substituents. This is a neutral phenol and has moderate acidity.
- **Compound 3**: Contains a NO₂ group (nitro group), which is an electron-withdrawing group (-I and -R effect). This will increase the acidity of phenol.
- **Compound 4**: Contains three NO₂ groups attached to the phenol. The presence of multiple electron-withdrawing groups will significantly increase the acidity due to their cumulative -I and -R effects.

4. **Compare Acidity**:
- The presence of the CH₃ group in Compound 1 decreases acidity.
- Compound 2 has no substituents and has moderate acidity.
- Compound 3 has one NO₂ group, which increases acidity.
- Compound 4, with three NO₂ groups, will have the highest acidity due to the strong electron-withdrawing effects of the three nitro groups.

5. **Conclusion**:
Based on the analysis, the compound with three NO₂ groups (Compound 4) is the most acidic.

### Final Answer:
The most acidic compound is **Compound 4** (with three NO₂ groups).