Arrange the following in increasing order of ligand field strength.
A. \(CO\)
B. \(NH_3\)
C. \(EDTA^{4-}\)
D. \(Cl^-\)
E. \(I^-\)
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → E, D, C, B, A
The splitting of d orbitals produced by a ligand measures its field strength; ligands arranged by increasing field strength form the spectrochemical series. Placing the five given ligands in it:
E. \( \ce{I^{-}} \) — first. The weakest ligand of the series.
D. \( \ce{Cl^{-}} \) — second. A weak halide ligand, a little stronger than \( \ce{I^{-}} \).
C. EDTA4− — third. Stronger than the halides and water.
B. \( \ce{NH3} \) — fourth. Just above edta4−.
A. CO — last. The strongest; it also accepts metal d electrons into its empty π* orbitals (back bonding).
NCERT (2026-27 edition):
Crystal Field Theory – “… 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.”