Assertion : Benzene diazonium salt on boiling with water forms phenol.
Reason : C - N bond is polar.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion
B. If both assertion and reason are true but reason is not the correct explanation of assertion
C. If assertion is true but reasonb is false
D. If both assertion and reason are false.

Explanation

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

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "Benzene diazonium salt on boiling with water forms phenol."
- Benzene diazonium salts, such as benzene diazonium chloride, can undergo hydrolysis when treated with water. The reaction leads to the formation of phenol and nitrogen gas (N2).

2. **Reaction Mechanism**:
- When benzene diazonium chloride is boiled with water, the nitrogen (N2) group is released, and a hydroxyl group (OH) is introduced in its place.
- The reaction can be summarized as:
\[ \text{C}_6\text{H}_5\text{N}_2\text{Cl} + \text{H}_2\text{O} \rightarrow \text{C}_6\text{H}_5\text{OH} + \text{N}_2 + \text{HCl} \]
- This confirms that the assertion is true.

3. **Understanding the Reason**:
- The reason states that "C - N bond is polar."
- In benzene diazonium salts, the carbon-nitrogen bond is indeed polar due to the difference in electronegativity between carbon and nitrogen. This polarity contributes to the reactivity of the diazonium group.

4. **Evaluating the Relationship**:
- While both the assertion and reason are true, the reason does not directly explain why boiling benzene diazonium salt with water produces phenol. The mechanism involves the loss of nitrogen gas and the substitution of the diazonium group with a hydroxyl group, which is not solely due to the polarity of the C-N bond.

5. **Conclusion**:
- Both the assertion and reason are true, but the reason is not a correct explanation of the assertion.

### Final Answer:
- The correct option is: **Both assertion and reason are true but reason is not a correct explanation of assertion.**