Cis and Trans Isomerism given three different groups around the reference plane In the following problem I am meant to deduce the molecules that are cis-trans isomers of each other.
This question does not make much sense in my head because I thought that cis/trans isomerism was only applied to configurational isomers if there were only two types of groups bonded to the carbon atoms in the carbon-carbon double bond i.e. the reference plane. Such that, if there are more than two groups bonded to the carbons in the reference plane then E/Z isomerism should be used. However, then I thought that cis/trans isomerism is a subcategory of E/Z isomerism and therefore I tried to work out the solution using the E/Z method of finding configurational isomers by finding the relative priorities based on the atomic numbers for the atoms attached to the carbon atoms on each side. Using this method I discovered, that the solution could only be 'A. X and Z' since X seems to be an 'E' isomer since its high and low priority groups are across from eachother and Z seems to be a 'Z' isomer since its high and low priority groups are on the same side. 

Am I on the right track?
Am I on the right track?


Generally, yes. For this question, yes but you have over thought this question.

For starters, any answer with Y can be totally eliminated as Y is neither cis nor trans. Now you are down to answers 'A.' and 'D.'

Here you correctly determined the E and Z configurations of molecules with identical functional groups, but could have saved yourself some effort if you had recognized W and Z are identical molecules that are inversions/180° rotations of each other. Thus it can't be D. and the answer is in fact:


  A.