Question -
Answer -
A ligand may contain one or more unsharedpairs of electrons which are called the donor sites of ligands. Now, dependingon the number of these donor sites, ligands can be classified as follows:
(a) Unidentate ligands: Ligandswith only one donor sites are called unidentate ligands. For e.g., 
, Cl− etc.(b) Didentateligands: Ligands that have two donor sites are called didentateligands. For e.g.,
(a) Ethane-1,2-diamine
(b) Oxalate ion
(c) Ambidentateligands:
Ligands that can attach themselves to thecentral metal atom through two different atoms are called ambidentate ligands.For example:
(a)
(The donor atom is N)
(The donor atom is oxygen)
(b)
(The donor atom is S)
(The donor atom is N)