Case: Read the passage and answer the following questions

Crystal field theory (CFT) describes the breaking of degeneracies of electron orbital states, usually d or f orbitals, due to a static electric field produced by a surrounding charge distribution (anion neighbours). This theory has been used to describe various spectroscopies of transition metal coordination complexes, in particular optical spectra (colours). CFT successfully accounts for some magnetic properties, colours, hydration enthalpies, and spinel structures of transition metal complexes, but it does not attempt to describe bonding.

Which of the following complexes shows zero crystal field stabilization energy?

[Fe(H₂O)₆]³⁺

[Fe(H₂O)₆]³⁺ 

x + 6(0) = 3

x = 3

Fe electronic configuration  [Ar]3d⁶4s²

Fe³⁺ electronic configuration [Ar]3d⁵

Due to this weak ligand 5 electrons exist as t_2g³ eg²

CFSE = 3 x (-0.4) + 2 x 0.6 = -1.2 + 1.2 = 0