Identify the complex with the largest crystal field splitting energy, otherwise known as Delta. So when it comes to Delta, remember that tetrahedral has the smallest venopahedrals in the middle and then square planar is the highest. Now if we take a look the first three each has iron connected to six ligands, so all of these are octahedral in nature.
The last one though has four chlorides connected to copper, so there's the potential of it being tetrahedral or square planar. So let's figure that one out first. So here this has to do with the copper plus one ion, because here it's trying to basically work with the four chloride ions. But since there's more negative charge, that's why we have a remainder of three minus neutral copper.
Its electron configuration is argon 4S13D10, remember, is an exception. Plus one means we've lost one electron from the highest shell number, so the 4S electron will be gone. So Copper one is Argon 3D10. We have a D10 ion, and because it's D10, that means that it is tetrahedral. Tetrahedral has the smallest crystal field slitting energy, so this would not be our answer.
It's going to be one of these three here they're all octahedral. So how do we determine? Well, remember for octahedral species, the ligand that attaches determines or effects our crystal field splitting energy. So all you have to remember is that Larry cannot enter the neighborhood. So here the strongest field ligand would give us the highest or largest crystal field splitting energy and cannot is the beginning of our memory tool.
So cyanide here would be the strongest field ligand when compared to water and ammonia. So here the answer would have to be option C. So C would be our answer. It would produce the largest crystal field splitting energy.