Which of the following species is not expected to be a ligand?

1.  NO

2.  NH4+

3.  NH2CH2CH2NH2

4.  CO

A chelating ligand has two or more binding donor atoms to a single metal ion


Here (4) denotes binding site.

thiosulphato (S2O32) is not a chelating ligand because geometrically it is 

not favourable for (S2O32) to chelate a metal ion.