Which order is correct about acidity?

Options

A. `CH_3 COOH gt C_6H_5COOH gt C_6H_5OH`
B. `C_6H_5COOH gt CH_3COOH gt C_6H_5OH`
C. `C_6H_5OH gt C_6H_5COO gt CH_3COOH`
D. `C_6H_5OH gt CH_3COOH gt C_6H_5 COOH`

Answer

To determine the correct order of acidity among acetic acid, benzoic acid, and phenol, we need to evaluate the stability of their conjugate bases and the influence of substituents on acidity.

### Step-by-Step Solution:

1. **Understanding Acidity**:
Acidity is determined by the ability of a compound to donate a proton (H⁺) and the stability of the resulting conjugate base. The more stable the conjugate base, the stronger the acid.

2. **Analyzing Benzoic Acid (C₆H₅COOH)**:
- Benzoic acid has a carboxyl group (COOH) attached to a benzene ring.
- When it donates a proton, it forms the benzoate ion (C₆H₅COO⁻).
- The benzoate ion is stabilized by resonance; the negative charge can be delocalized over the two oxygen atoms and the benzene ring. This resonance stabilization makes benzoic acid the most acidic among the three.

3. **Analyzing Acetic Acid (CH₃COOH)**:
- Acetic acid also has a carboxyl group but is attached to a methyl group (CH₃).
- When it donates a proton, it forms the acetate ion (CH₃COO⁻).
- The methyl group is an electron-donating group, which slightly destabilizes the acetate ion compared to the benzoate ion. Therefore, acetic acid is less acidic than benzoic acid but more acidic than phenol.

4. **Analyzing Phenol (C₆H₅OH)**:
- Phenol has a hydroxyl group (OH) attached to a benzene ring.
- When it donates a proton, it forms the phenoxide ion (C₆H₅O⁻).
- The phenoxide ion is stabilized by resonance, but the negative charge is located on the oxygen atom, which is less electronegative than the carbon atoms in the benzene ring. This results in less effective resonance stabilization compared to the benzoate ion. Therefore, phenol is the least acidic among the three.

5. **Conclusion**:
Based on the analysis above, the order of acidity from strongest to weakest is:
- **Benzoic Acid (C₆H₅COOH) > Acetic Acid (CH₃COOH) > Phenol (C₆H₅OH)**.

### Final Answer:
The correct order of acidity is:
**Benzoic Acid > Acetic Acid > Phenol**.