Assertion The p - isomer of dichlorobenzene has higher m.p than o-and m isomer
Reason p-isomer is symmetrical and thus shows more closely packed structure .

Options

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

Answer

**Step-by-step Solution:**

1. **Understanding the Isomers:**
- We have three isomers of dichlorobenzene: ortho (o), meta (m), and para (p).
- The structures of these isomers differ based on the positions of the chlorine atoms on the benzene ring.

2. **Analyzing the Assertion:**
- The assertion states that the para isomer of dichlorobenzene has a higher melting point than the ortho and meta isomers.
- To evaluate this, we need to consider the structural differences and how they affect melting points.

3. **Considering Symmetry:**
- The para isomer is symmetrical, meaning that the chlorine atoms are positioned opposite each other on the benzene ring.
- This symmetry allows for a more uniform distribution of electron density, leading to stronger intermolecular forces.

4. **Comparing Packing Efficiency:**
- The para isomer can pack more closely in a solid state compared to the ortho and meta isomers.
- Ortho isomers have steric hindrance due to the proximity of the two chlorine atoms, which disrupts close packing.
- Meta isomers, while less hindered than ortho, still do not achieve the same level of packing efficiency as para isomers.

5. **Conclusion on Melting Points:**
- Due to the higher packing efficiency and symmetry of the para isomer, it experiences stronger intermolecular forces, resulting in a higher melting point.
- Therefore, the assertion is true.

6. **Analyzing the Reason:**
- The reason states that the para isomer is symmetrical and thus shows a more closely packed structure.
- This is indeed a correct explanation for why the para isomer has a higher melting point compared to the ortho and meta isomers.

7. **Final Evaluation:**
- Both the assertion and reason are true, and the reason correctly explains the assertion.
- Hence, the correct conclusion is that both the assertion and reason are true, and the reason is the correct explanation for the assertion.

**Final Answer:**
Both assertion and reason are true, and the reason is the correct explanation of the assertion.

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