Statement I: NO2− and SCN− are ambidentate ligands.
Statement II: A ligand which has two different donor atoms, either of which can bind to the metal ion in a complex, is called an ambidentate ligand.
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Both Statement I and Statement II are correct and Statement II is the correct explanation of Statement I.
A unidentate ligand binds the metal through one donor atom. If such a ligand carries two different donor atoms and can use either of them, it is called ambidentate.
Statement I: NO2− and SCN− are ambidentate ligands. — True. \( \ce{NO2^-} \) can bind through nitrogen (M–NO2) or through oxygen (M–ONO); thiocyanate can bind through nitrogen (M–NCS) or through sulphur (M–SCN).
Statement II: A ligand which has two different donor atoms, either of which can bind to the metal ion in a complex, is called an ambidentate ligand. — True. This is the definition of an ambidentate ligand.
Why Statement II explains Statement I? Each of \( \ce{NO2^-} \) and \( \ce{SCN^-} \) has two different donor atoms (N and O; N and S), either of which can attach to the metal. They fit the definition in Statement II, and that is the reason they are called ambidentate. The two ways of binding give rise to linkage isomerism.
NCERT (2026-27 edition):
5.2 Definitions of Some Important Terms Pertaining to Coordination Compounds – “… Ligand which has two different donor atoms and either of the two ligetes in the complex is called ambidentate ligand. Examples of such ligands are the NO2– and SCN– ions. NO2– ion can coordinate either through nitrogen or through oxygen to a central metal atom/ion.”
5.4.3 Linkage Isomerism – “Linkage isomerism arises in a coordination compound containing ambidentate ligand. A simple example is provided by complexes containing the thiocyanate ligand, NCS–, which may bind through the nitrogen to give M–NCS or through sulphur to give M–SCN.”