Explanation:
The three options are:
1) Both Cl in the same carbon
2) One Cl in each C and both in the same side of the double bond (cis )
2) One Cl in each C and both in the oposite sides of the double bond (trans )
Options 2 and 3 are geometrical isomers and will generate the same products, so this options will be X and Z. Therefore Y is the one described in option 1.
Now, having the two electronegative atoms (Cl) in the same side will create a dipole moment but if they are oposed, the dipole moment will be canceled. Being that said we can affirm that the option 2) is Z and the option 3) is X
In the figure you can see the structures of X, Y and Z from top to bottom.
