Final answer:
The double bond in a molecule is best described by the Cis-Trans Isomer designation when identical groups are present, and by the E-Z Isomer designation for different substituents requiring prioritization of groups.
Step-by-step explanation:
The stereochemistry designation that best describes the double bond in the molecule provided would be the Cis-Trans Isomer or the E-Z Isomer, depending on the substituents attached to the double bond. Cis-trans isomers occur when two identical substituents are on the same side (cis) or opposite sides (trans) of a double bond. However, when there are different substituents that require prioritization, the E-Z notation is used. The E designation means the higher priority groups are on opposite sides of the double bond (entgegen in German), and the Z designation means the higher priority groups are on the same side (zusammen in German).
For molecules like 2-butene, where you have two identical groups on each carbon atom of the double bond, the Cis-Trans Isomer designation can be utilized directly without further need for prioritization. With complex examples involving a double bond with different substituents, the E-Z notation based on the Cahn-Ingold-Prelog priority rules is required to accurately describe the isomer.