Assertion: It is difficult to replace chlorine by `-OH` in chlorobenzene in comparison to that in chloroethane
Reason: Chlorine-carbon (C-Cl) bond in chlorobenzene has a partial double bond character due to resonance.

Options

A. Assertion and reason both are correct and reason is correct explanation of assertion
B. Assertion and reason both are wrong statements
C. Assertion is correct but reason is wrong statement
D. Assertion is wrong but reason is correct statement.

Explanation

To analyze the assertion and reason provided in the question, we will break down the concepts involved in the comparison of chlorobenzene and chloroethane regarding the replacement of chlorine by hydroxyl (-OH) group.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that it is difficult to replace chlorine by -OH in chlorobenzene compared to chloroethane.
- We need to consider the structure and bonding in both compounds.

2. **Analyzing Chlorobenzene**:
- Chlorobenzene has a chlorine atom attached to a benzene ring. The C-Cl bond in chlorobenzene is influenced by resonance.
- The resonance in chlorobenzene leads to a partial double bond character in the C-Cl bond, making it stronger and less reactive towards nucleophilic substitution.

3. **Analyzing Chloroethane**:
- Chloroethane (C2H5Cl) has a chlorine atom attached to a saturated carbon chain. The C-Cl bond in chloroethane is a single bond and does not have resonance stabilization.
- This makes the C-Cl bond in chloroethane more susceptible to nucleophilic attack, allowing for easier substitution of chlorine by -OH.

4. **Comparing Reactivity**:
- Due to the resonance stabilization in chlorobenzene, the C-Cl bond is stronger and less reactive compared to the C-Cl bond in chloroethane.
- Therefore, it is indeed more difficult to replace chlorine with -OH in chlorobenzene than in chloroethane.

5. **Understanding the Reason**:
- The reason states that the C-Cl bond in chlorobenzene has a partial double bond character due to resonance.
- This statement is correct and explains why the substitution reaction is more challenging in chlorobenzene.

6. **Conclusion**:
- The assertion is true, and the reason is also true. The reason correctly explains the assertion.

### Final Answer:
- Both the assertion and reason are true, and the reason correctly explains the assertion.