Arrange the following ligands in the increasing order of their field strength:
(A) \( en \)
(B) \( edta^{4-} \)
(C) \( S^{2-} \)
(D) \( OH^- \)
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (C), (D), (B), (A)
The field strength of a ligand is its ability to split the d orbitals of the metal ion; the larger the splitting \( \Delta_o \), the stronger the field. Ligands arranged in order of increasing field strength form the spectrochemical series, found by experiment from the light absorbed by their complexes. Halide and sulphide ions are at the weak end, neutral nitrogen donors such as \( \ce{NH3} \) and en are near the strong end, and \( \ce{CN^-} \) and CO are the strongest.
Of the four, \( \ce{S^2-} \) is the weakest, then \( \ce{OH^-} \), then edta4−, and en is the strongest.
Shortcut: \( \ce{S^2-} \) is the weakest and en the strongest, so the order starts with (C) and ends with (A): Options (1) and (4). Since \( \ce{OH^-} \) is a weaker ligand than edta4−, (D) comes before (B), which leaves Option (1).
NCERT (2026-27 edition):
Crystal Field Theory – …
