Here it says which set of D orbitals below will interact the most with the ammonia ligands within this coordination complex. All right. So remember this is our complex ion portion and this is what we care about. The chlorine over here is just a counter ion.
Now here we have 6 ammonia molecule ligands attached to our iron. So this is an octahedral complex and when it comes to octahedral complexes, the greatest interactions are happening along the axis or on the axes. And that only happens for two types of orbitals and there would be Dx2-y2 and Dz2.
If we look at our options, the only one that has only those two orbitals and nothing else would be option E. Here option E would be our final answer.