Assertion: The `pK_(a)` of acetic acid is lower than that of phenol.
Reason : Phenoxide ion is more resonance sabilised.

Options

A. If Both assertion and reason are true reason is the correct explation of the assertion.
B. If Both assertion and reason are true but reason is not the correct explation of the assertion.
C. If assertion is true but reason is false.
D. If assertion is false but reason is true.

Explanation

To solve the given question, we need to analyze both the assertion and the reason provided:

### Step 1: Understand the Assertion
The assertion states that the pKa of acetic acid is lower than that of phenol.

- **Acetic Acid (CH3COOH)** is a weak acid that can dissociate to form acetate ions (CH3COO⁻) and protons (H⁺).
- **Phenol (C6H5OH)** is also a weak acid that can dissociate to form phenoxide ions (C6H5O⁻) and protons (H⁺).

### Step 2: Compare the Acid Strength
To compare the strength of these acids, we look at their dissociation constants (Ka).

- A lower pKa value indicates a stronger acid.
- The pKa is related to the Ka by the equation:
\[ pKa = -\log(Ka) \]

### Step 3: Determine the Ka Values
From known data:
- The Ka of acetic acid is approximately 1.76 x 10⁻⁵.
- The Ka of phenol is approximately 1.0 x 10⁻¹⁰.

Since:
\[ Ka_{acetic\ acid} > Ka_{phenol} \]
This implies:
\[ pKa_{acetic\ acid} < pKa_{phenol} \]
Thus, the assertion is correct.

### Step 4: Understand the Reason
The reason states that the phenoxide ion is more resonance stabilized.

- The phenoxide ion (C6H5O⁻) has a negative charge that can be delocalized over the aromatic ring through resonance. This stabilization makes phenol a weaker acid compared to acetic acid.
- In acetic acid, the acetate ion (CH3COO⁻) does not have the same level of resonance stabilization as the phenoxide ion.

### Step 5: Analyze the Relationship
While both the assertion and the reason are true, the reason does not explain why acetic acid has a lower pKa than phenol. The reason discusses the stability of the phenoxide ion but does not directly relate to the strength of acetic acid.

### Conclusion
- **Assertion**: True (pKa of acetic acid is lower than that of phenol)
- **Reason**: True (phenoxide ion is more resonance stabilized)
- The reason is not the correct explanation for the assertion.

### Final Answer
The correct option is B: Both assertion and reason are true, but the reason is not the correct explanation of the assertion.

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