Among the following, the stronger acid in basic medium is

Options

A. Aniline
B. Phenol
C. Ammonia
D. Benzene

Answer

To determine which is the stronger acid in a basic medium among the given options (aniline, phenol, ammonia, and benzene), we can analyze each compound and its corresponding conjugate base.

### Step-by-Step Solution:

1. **Identify the Compounds**:
- The compounds to analyze are aniline, phenol, ammonia, and benzene.

2. **Understand Basic Medium**:
- In a basic medium, hydroxide ions (OH⁻) are present, which can abstract protons (H⁺) from acids.

3. **Determine Conjugate Bases**:
- For each compound, we will find the conjugate base formed when a proton is removed by OH⁻:
- **Aniline (C₆H₅NH₂)**:
- When OH⁻ abstracts a proton, it forms anilide (C₆H₅NH⁻).
- **Phenol (C₆H₅OH)**:
- When OH⁻ abstracts a proton, it forms phenoxide ion (C₆H₅O⁻).
- **Ammonia (NH₃)**:
- When OH⁻ abstracts a proton, it forms amide ion (NH₂⁻).
- **Benzene (C₆H₆)**:
- When OH⁻ abstracts a proton, it forms a phenyl anion (C₆H₅⁻).

4. **Stability of Conjugate Bases**:
- The strength of an acid is related to the stability of its conjugate base. More stable conjugate bases correspond to stronger acids.
- **Benzene**: The phenyl anion (C₆H₅⁻) is less stable because the negative charge is on an sp² carbon that is not involved in resonance with the ring.
- **Ammonia**: The amide ion (NH₂⁻) is also not stabilized by resonance.
- **Aniline**: The anilide ion (C₆H₅NH⁻) has some resonance stabilization, but nitrogen is less electronegative than oxygen.
- **Phenol**: The phenoxide ion (C₆H₅O⁻) is stabilized by resonance, and the negative charge is held by the more electronegative oxygen atom, making it more stable.

5. **Comparison of Stability**:
- Among the conjugate bases:
- Phenoxide ion (C₆H₅O⁻) is the most stable due to resonance and the electronegativity of oxygen.
- Anilide ion (C₆H₅NH⁻) is less stable than phenoxide but more stable than the other two.
- Amide ion (NH₂⁻) and phenyl anion (C₆H₅⁻) are the least stable.

6. **Conclusion**:
- Since phenol forms the most stable conjugate base (phenoxide ion), it is the strongest acid in a basic medium among the given options.

### Final Answer:
The stronger acid in basic medium is **Phenol**.