Which one of the following will yield the highest splitting of d orbitals?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → \(CN^–\)
The size of the crystal field splitting depends on the field produced by the ligand; ligands arranged by field strength form the spectrochemical series. Of the given ligands, CN− is the strongest field ligand and produces the largest splitting.
Shortcut: The given ligands in order: \( \ce{S^{2-}} \) < \( \ce{OH^{-}} \) < edta4− < \( \ce{CN^{-}} \); \( \ce{CN^{-}} \) is near the strong end of the series.
NCERT (2026-27 edition):
Crystal Field Theory – “… The crystal field splitting, Δo, depends upon the field produced by the ligand and charge on the metal ion. Some ligands are able to produce strong fields in which case, the splitting will be large whereas others produce weak fields and consequently result in small splitting of d orbitals. In general, ligands can be arranged in a series in the order of increasing field strength as given below:
I– < Br– < SCN– < Cl– < S2– < F– < OH– < C2O42– < H2O < NCS– < edta4– < NH3 < en < CN– < CO
Such a series is termed as spectrochemical series. It is an experimentally determined series based on the absorption of light by complexes with different ligands.”