Which of the following will have zero dipole moment?

Options

A. (a) cis, `-1,2`-Dichloroethene
B. (b) trans `-1,2`-Dichloroethene
C. (c) Dichloromethane
D. (d) Dibromomethane

Explanation

To determine which of the given compounds has a zero dipole moment, we will analyze the structures and the molecular geometry of each option.

### Step-by-Step Solution:

1. **Identify the Compounds**: We need to analyze four compounds, which are likely to be isomers of dichloroethene and other related compounds.

2. **Draw the Structure of Cis-1,2-Dichloroethene**:
- The structure of cis-1,2-dichloroethene (C2H2Cl2) has both chlorine atoms on the same side of the double bond.
- This creates a polar molecule because the dipole moments from the C-Cl bonds do not cancel out. Therefore, the dipole moment is not zero.

3. **Draw the Structure of Trans-1,2-Dichloroethene**:
- The structure of trans-1,2-dichloroethene has the chlorine atoms on opposite sides of the double bond.
- In this case, the dipole moments from the C-Cl bonds are equal in magnitude but opposite in direction, resulting in a net dipole moment of zero.

4. **Draw the Structure of Dichloromethane**:
- The structure of dichloromethane (CH2Cl2) has two chlorine atoms and two hydrogen atoms attached to a central carbon atom.
- The dipole moments from the C-Cl bonds do not cancel out due to the tetrahedral geometry, resulting in a net dipole moment that is not zero.

5. **Draw the Structure of Dibromomethane**:
- The structure of dibromomethane (CH2Br2) is similar to dichloromethane but with bromine atoms.
- Like dichloromethane, the dipole moments from the C-Br bonds do not cancel out, resulting in a net dipole moment that is not zero.

6. **Conclusion**: After analyzing all four compounds, we find that only trans-1,2-dichloroethene has a zero dipole moment due to the cancellation of dipole moments.

### Final Answer:
The compound that has a zero dipole moment is **trans-1,2-dichloroethene**.

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