The correct order of melting points of dichlorobenzene is

Options

A.
B.
C.
D.

Answer

To determine the correct order of melting points of the isomers of dichlorobenzene (ortho, meta, and para), we need to consider the structural characteristics and symmetry of each isomer.

### Step-by-Step Solution:

1. **Identify the Isomers**:
- **Ortho-dichlorobenzene**: Chlorine atoms are adjacent to each other on the benzene ring.
- **Meta-dichlorobenzene**: Chlorine atoms are separated by one carbon atom on the benzene ring.
- **Para-dichlorobenzene**: Chlorine atoms are opposite each other on the benzene ring.

2. **Assess Symmetry**:
- The para isomer is symmetrical, meaning it has a balanced distribution of charge and shape. This symmetry allows for better packing in the solid state, leading to stronger intermolecular forces.

3. **Intermolecular Forces**:
- The melting point of a compound is influenced by the strength of intermolecular forces. The more symmetrical the molecule, the stronger the intermolecular forces due to better packing in the crystal lattice.
- Para-dichlorobenzene, being symmetrical, has stronger intermolecular forces compared to the ortho and meta isomers.

4. **Comparison of Ortho and Meta**:
- Both ortho and meta isomers are less symmetrical than the para isomer. However, the ortho isomer has steric hindrance due to the proximity of the two chlorine atoms, which can disrupt packing in the crystal lattice.
- The meta isomer, while also less symmetrical, does not have the same steric hindrance as the ortho isomer.

5. **Conclusion**:
- Based on symmetry and intermolecular forces, the order of melting points from highest to lowest is:
- **Para-dichlorobenzene > Ortho-dichlorobenzene > Meta-dichlorobenzene**.

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