Question

which structure has a dipole moment?
neither structure has a dipole moment
both structures have a dipole moment

Explanation:

Step1: Recall dipole - moment concept

A molecule has a dipole moment when there is a net separation of charge due to electronegativity differences and non - symmetric molecular geometry. Chlorine is more electronegative than hydrogen.

Step2: Analyze first structure

In the first structure (cis - 1,2 - dichloroethene), the two chlorine atoms are on the same side of the double bond. The bond dipoles due to the C - Cl bonds do not cancel out because of the non - symmetric arrangement around the double bond. So, it has a non - zero dipole moment.

Step3: Analyze second structure

In the second structure (trans - 1,2 - dichloroethene), the two chlorine atoms are on opposite sides of the double bond. The bond dipoles due to the C - Cl bonds are equal in magnitude but opposite in direction, and they cancel each other out. So, it has a zero dipole moment.

Answer:

The first structure has a dipole moment.