Which one of the following complexes shows the most complex splitting pattern energy? Remember this occurs with square planar complexes and if we look at our options, B&D are both out because in both we have 6 donor atoms connecting to our metal cation. Those could not give us a square planar complex.
The answer is going to be either A or C because in both of those we have 4 logins which have the potential of being either tetrahedral or square planar. In the first one, if we take a look at the cadmium ion, it's cadmium 2 plus its electron configuration when you look at it would be Krypton 4D10. Now here it is AD10 ion. And remember if you're D10 you are tetrahedral O. This will not give us the correct geometry.
For C we have nickel here connected to formonias which are neutral. So the two plus charge is coming from the nickel itself. If we do its electron configuration it would be argon 3D8. Now it is a D8 ion and that means that its geometry is square planar.
So option C would give us a squared planar geometry which results in the most complex splitting pattern energy.