Two things to consider here: the identity of the substituents and their arrangement around the central atom (Xe). A zero dipole moment results when the various dipoles of the bonds in the molecule cancel eachother out. This requires symmetry, which we have in abundance in XeF4. Each Xe-F bond has an identical dipole, but each as cancelled out by the bond opposite it, so the sum of dipoles from Xe-F bonds is zero. Also we need to consider the lone pairs, but as noted earlier, they are directly opposed to each other so it follows that they will cancel each other out too.
So the answer is XeF4. I hope this helps.
