The stabilisation of coordination compounds due to chelation is called the chelate effect. Which of the following is the most stable complex species?
Chelate effect is predominant in polydentate ligands as they form stronger complexes. A polydentate ligand has more than one place of attachment which makes it very stable. The only polydentate ligand in the given options is oxalate(bidentate) so it will form the most stable complex.