In an acidic medium ………………….. behaves as the strongest base (nitrobenzen. Aniline, phenol),

Answer

To determine which compound behaves as the strongest base in an acidic medium among nitrobenzene, aniline, and phenol, we can analyze the basicity of each compound based on their functional groups and the effects of substituents.

### Step-by-Step Solution:

1. **Understanding Basicity**:
Basicity refers to the ability of a compound to accept protons (H⁺ ions). In general, the presence of electron-donating groups increases basicity, while electron-withdrawing groups decrease it.

**Hint**: Remember that electron-donating groups (like alkyl groups) enhance basicity, while electron-withdrawing groups (like nitro groups) reduce it.

2. **Analyzing Nitrobenzene**:
Nitrobenzene has a nitro group (NO₂), which is a strong electron-withdrawing group. This reduces the electron density on the benzene ring and makes it less likely to donate electrons or accept protons, thus acting as a weak base.

**Hint**: Identify the functional groups in each compound and their effects on electron density.

3. **Analyzing Phenol**:
Phenol has a hydroxyl group (–OH) attached to the benzene ring. When phenol loses a hydrogen ion (H⁺), it forms the phenoxide ion, which is stabilized by resonance. However, phenol itself is still considered a weak acid rather than a strong base.

**Hint**: Consider the stability of the conjugate base formed when the compound loses a proton.

4. **Analyzing Aniline**:
Aniline contains an amino group (–NH₂), which has a lone pair of electrons on the nitrogen atom. This lone pair can be donated to accept protons, making aniline a weak base. Although the lone pair can participate in resonance with the benzene ring, it still allows aniline to act as a base.

**Hint**: Look for lone pairs on atoms that can donate electrons to determine basicity.

5. **Comparing Basicity**:
- Nitrobenzene: Weak base due to the electron-withdrawing nitro group.
- Phenol: Weak acid due to the stabilization of the phenoxide ion but not a strong base.
- Aniline: Weak base, but stronger than both nitrobenzene and phenol due to the presence of the electron-donating amino group.

6. **Conclusion**:
Among the three compounds, aniline behaves as the strongest base in an acidic medium due to the presence of the amino group that can donate a lone pair of electrons.

**Final Answer**: Aniline is the strongest base among nitrobenzene, aniline, and phenol.