If we consider 1 and 2 as priority, then which of the following is Z?
Select the atom/group with higher priority on each double bounded carbon. If the atoms/groups of higher priority (denoted by 1) on each carbon are on the same side of the double bond, the isomer is assigned the configuration Z (from the German word, Zusammen, meaning together). On the other hand, if the atoms/groups of higher priority on each carbon are on the opposite sides of the double bond, the isomer is assigned the configuration E (from the German word Entgegan, meaning against).
Where (1) and (2) represent the atoms (groups) of higher and lower priority respectively.