What is meant by unidentate,didentate and ambidentate ligands? Give two examples for each.

(N/A) ligand may contain one or more unshared pairs of electrons which are called the donor sites of ligands. Depending on the number of these donor sites,ligands can be classified as follows:
$(a)$ Unidentate ligands: Ligands with only one donor site are called unidentate ligands. For example,$NH_3$ and $Cl^-$.
$(b)$ Didentate ligands: Ligands that have two donor sites are called didentate ligands. For example,$H_2N-CH_2-CH_2-NH_2$ (ethane$-1,2-$diamine) and $C_2O_4^{2-}$ (oxalate ion).
$(c)$ Ambidentate ligands: Ligands that can attach themselves to the central metal atom through two different atoms are called ambidentate ligands. For example:
$1. NO_2^-$ (nitro,donor atom is $N$) and $ONO^-$ (nitrito,donor atom is $O$)
$2. SCN^-$ (thiocyanate,donor atom is $S$) and $NCS^-$ (isothiocyanate,donor atom is $N$)