Final answer:
A cis isomer is polar due to the uneven distribution of electron density, while a trans isomer is non-polar because the dipole moments cancel out.
Step-by-step explanation:
A cis isomer is polar because similar substituents are on the same side of the molecule, creating an uneven distribution of electron density. Conversely, a trans isomer is non-polar as substituents are on opposite sides, allowing the dipole moments to cancel out, leading to an even distribution of electron density. Substantial energy in the form of heat or light is often required to convert one isomer to the other.