What type of ligand is the oxalate ion?

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

The anti-cancer drug cisplatin contains which of the following ligands?

Which of the following ligands is expected to be bidentate?

The sum of the coordination number and the oxidation number of the metal $M$ in the complex $[M(en)_2(C_2O_4)]Cl$ (where $en$ is ethylenediamine) is:

Homoleptic complexes among the following are:
$(A)$ $K_3[Al(C_2O_4)_3]$
$(B)$ $[CoCl_2(en)_2]^{+}$
$(C)$ $K_2[Zn(OH)_4]$