Which of the following is incorrect for cis-but-`2`-ene relative to trans-but-`2`-ene?

Options

A. It has higher dipole moment.
B. It has higher boiling point.
C. It has higher melting point.
D. All of these

Explanation

To determine which statement is incorrect for cis-but-2-ene relative to trans-but-2-ene, we need to analyze the properties of both isomers based on their molecular structure and how this affects their physical properties.

### Step-by-Step Solution:

1. **Identify the Structure of the Isomers**:
- **Cis-but-2-ene**: In this isomer, the two methyl groups (CH₃) are on the same side of the double bond.
- **Trans-but-2-ene**: In this isomer, the two methyl groups are on opposite sides of the double bond.

2. **Dipole Moment Comparison**:
- **Cis-but-2-ene** has a dipole moment because the two methyl groups on the same side create an uneven distribution of charge.
- **Trans-but-2-ene** has a dipole moment of zero because the dipoles from the two methyl groups cancel each other out due to their opposite positions.

3. **Boiling Point Comparison**:
- The presence of a dipole moment in **cis-but-2-ene** leads to stronger intermolecular attractions (dipole-dipole interactions), resulting in a higher boiling point compared to **trans-but-2-ene**.

4. **Melting Point Comparison**:
- The packing efficiency of molecules affects their melting points. **Trans-but-2-ene** can pack more efficiently in a crystal lattice due to its symmetrical structure, leading to a higher melting point.
- **Cis-but-2-ene**, being less symmetrical, does not pack as well, resulting in a lower melting point.

5. **Conclusion**:
- Based on the analysis:
- **Cis-but-2-ene has a higher boiling point than trans-but-2-ene** (True).
- **Cis-but-2-ene has a dipole moment, while trans-but-2-ene does not** (True).
- **Cis-but-2-ene has a higher melting point than trans-but-2-ene** (False).

Thus, the incorrect statement is that **cis-but-2-ene has a higher melting point than trans-but-2-ene**.