Which of the following ligands is correctly matched with its...

Ethane-1,2-diamine ($H_2N-CH_2-CH_2-NH_2$) is a didentate ligand with two nitrogen donor atoms.

Thiocyanate ion ($SCN^-$) is an ambidentate ligand (monodentate) that can coordinate through either sulfur or nitrogen.

Oxalate ion ($C_2O_4^{2-}$) is a didentate ligand with two oxygen donor atoms.

Nitrite ion ($NO_2^-$) is an ambidentate ligand (monodentate) that can coordinate through either nitrogen or oxygen.

Therefore, the oxalate ion is correctly matched with its denticity and donor atoms.

Answer: Oxalate ion : Didentate ligand with two oxygen donor atoms