Which of the following is correct about the nature of ligand?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → CN is an ambidentate ligand
Ligands are classed by the number of donor atoms they use. A unidentate ligand binds through one donor atom, a didentate ligand through two and a polydentate ligand through several. A di- or polydentate ligand that binds one metal ion through two or more donor atoms at once forms a ring and is a chelating ligand. An ambidentate ligand has two different donor atoms but binds through only one of them at a time.
The cyanide ion, \( \ce{[:C#N:]-} \), has a lone pair on carbon and one on nitrogen. It can bind through carbon (M–CN, cyanido) or through nitrogen (M–NC, isocyanido), so it is an ambidentate ligand, like \( \ce{NO2-} \) and \( \ce{SCN-} \).
Why the other options are incorrect
Option (2) Ethylenediaminetetraacetate ion (\( \ce{EDTA^4-} \)) is tetradentate ligand — Incorrect. EDTA binds through two nitrogen and four oxygen atoms, so it is hexadentate.
Option (3) \( \ce{CH3NH2} \) is a bidentate ligand — Incorrect. Methylamine has only one donor atom, the nitrogen with its lone pair, so it is unidentate.
Option (4) \( \ce{C2O4^2-} \) is not a Chelating ligand — Incorrect. The oxalate ion binds through two oxygen atoms at once and forms a five-membered ring with the metal, so it is a chelating ligand.
NCERT (2026-27 edition):
Definitions of Some Important Terms Pertaining to Coordination Compounds – …
