For which of the following molecules(s) has /have significant $\mu \ne 0$.

 

Assuming planar structure, hydroquinone has two conformations as shown in the following.

The structure (I) is expected to have zero dipole moment whereas the structure (II) is expected to have a dipole moment. This conclusion may be derived based on the vector addition of components of dipole moment. The above facts are also applicable to 1, 4-benzenedithiol (structure iv).