When degenerate d-orbitals of an isolated atom/ion come under influence of magnetic field of ligands — Coordination Compounds Chemistry Question

Question

When degenerate d-orbitals of an isolated atom/ion come under influence of magnetic field of ligands, the degeneracy is lost. The two set t2g (d_xy, d_yz, d_zx) and eg (d_z^2, d_x^2-y^2) are either stabilized or destabilized depending upon the nature of magnetic field. It can be expressed diagrammatically as : [SEE DIAGRAM] Value of CFSE depends upon nature of ligand and a spectrochemical series has been made experimentally, for tetrahedral complexes, \Delta is about 4/9 times to \Delta_o (CFSE for octahedral complex). This energy lies in visible region and i.e., why electronic transition are responsible for colour. Such transitions are not possible with d^0 and d^10 configuration.