Which among the following is the correct order of melting point ?

Options

A.
B.
C.
D.

Answer

To determine the correct order of melting points for ortho-, meta-, and para-substituted chlorobenzene, we will analyze the factors that influence melting points, particularly the molecular packing and dipole moments.

### Step-by-Step Solution:

1. **Understanding the Compounds**:
- We have three isomers of chlorobenzene: ortho-chlorobenzene, meta-chlorobenzene, and para-chlorobenzene. Each has the chlorine substituent at different positions on the benzene ring.

2. **Factors Affecting Melting Point**:
- The melting point of a substance is influenced by the strength of intermolecular forces and how well the molecules can pack together in a solid state.
- Stronger intermolecular forces and tighter packing lead to higher melting points.

3. **Analyzing Dipole Moments**:
- The dipole moment of a molecule affects its intermolecular attractions. In chlorobenzene, the presence of the chlorine atom creates a dipole due to its electronegativity.
- In ortho and meta isomers, the dipole moments are affected by the relative positions of the chlorine atoms. The ortho isomer has two chlorine atoms closer together, which can lead to stronger dipole-dipole interactions.

4. **Comparing Molecular Packing**:
- The para isomer has a symmetrical structure that allows for better packing in the solid state, leading to stronger van der Waals forces.
- The ortho isomer, while it has stronger dipole interactions, may not pack as efficiently as the para isomer.
- The meta isomer has the least effective packing and dipole interactions compared to the other two.

5. **Conclusion on Melting Points**:
- Based on the analysis, we can conclude that the order of melting points is:
- **Para-chlorobenzene > Ortho-chlorobenzene > Meta-chlorobenzene**.

### Final Answer:
The correct order of melting points is:
**Para-chlorobenzene > Ortho-chlorobenzene > Meta-chlorobenzene**.