CHEMISTRY COMMUNITY

The question asks which of the following ligands can be polydentate? CO3 2- was said to be mono or bidentate and oxalate was said to be bidentate. For CO3 2-, why can it be mono or bidentate? For oxalate, where are the two places that the ligand can bind to the central metal? Is it the two oxygens that are single bonded or double bonded or either? I'm just a little confused because all the oxygens have lone pairs.

I believe CO3 2- was said to be mono or bidentate because either one or both of the oxygen atoms can bind to the central atom. Oxalate is a bidentate ligand because two oxygen atoms bind to the central atom. There are four oxygen atoms but the ion is planar and so the oxygen atoms are pointing in different directions meaning the central metal can only bond to two of them.