Question

Is $CO$ a monodentate ligand?

Answer 1

Hint: Ligands are neutral molecules or ions or atoms or groups of atoms which are attached directly to the central metal ion or atom through coordinate bonds in the complex ion. A ligand is a species that is capable of donating a pair of electrons to a metal. The nature of metal-ligand bonding may range from covalent to ionic.

Complete answer:
The term denticity refers to the number of donor groups in a ligand which bind to the central atom in a coordination complex. Monodentate ligands are the ligands which coordinate to only one site of a metal ion i.e. in these types of ligands, only one pair of electrons can be donated to the metal ion. Monodentate ligands are sometimes called unidentate ligands because the denticity of monodentate ligands is one. Monodentate ligands are also called one-toothed ligands. Carbon monoxide is a monodentate ligand as it is a lewis base that donates a single pair of electrons to a metal atom. The term monodentate means one tooth, referring to the ligand binding to the center through only one atom.
Therefore, $CO$ is a monodentate ligand.

Note:
Remember that ligands should have the capability to donate their lone pair of electrons to the central metal atom or ion and form coordinate bonds with it. Ligands behave as lewis bases while the metal atom or ion behaves as a lewis acid, and an lewis acid-base reaction takes place in between them to form a coordination compound.