When degenerate d-orbitals of an isolated atom/ion come under influence of magnetic field of ligands, the degeneray is lost. The two set `t_(2g)(d_(xy),d_(yz),d_(xz)) and e_(g) (d_(x^(2))-d_(x^(2)-y^(2))` are either stabilized or destabilized depending upon the nature of magnetic field. it can be expressed diagrammatically as:

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_(0)` (CFSE for octahedral complex). this energy lies in visible region and i.e., why electronic transition are responsible for colour. such transition are not possible with `d^(0) and d^(10)` configuration.
Q. `Cr^(3+)` form four complexes with four different ligands which are `[Cr(Cl)_(6)]^(3-), [Cr(H_(2)O)_(6)]^(3+)`,
`[Cr(NH_(3))_(6)]^(3+) and [Cr(CN)_(6)]^(3-)`, the order of CFSE `(Delta_(0))` in these complexes in the order:

Options

A. `[CrCl_(6)]^(3-)=[Cr(H_(2)O)_(6)]^(3+)=[Cr(NH_(3))_(6)]^(3+)=[Cr(CN)_(6)]^(3-)`
B. `[CrCl_(6)]^(3-) lt [Cr(H_(2)O)_(6)]^(3+) lt [Cr(NH_(3))_(6)]^(3+) lt [Cr(CN)_(6)]^(3-)`
C. `[CrCl_(6)]^(3-) gt [Cr(H_(2)O)_(6)]^(3+) gt [Cr(NH_(3))_(6)]^(3+) gt [Cr(CN)_(6)]^(3-)`
D. `[CrCl_(6)]^(3-) lt [Cr(H_(2)O)_(6)]^(3+) = [Cr(NH_(3))_(6)]^(3+) lt [Cr(CN)_(6)]^(3-)`

Answer

B