Solution

The oxalate ion, $C_2O_4^{2-}$, is a bidentate ligand: it binds to the metal through two oxygen atoms.
There are three oxalate ligands, each forming two bonds with Ni.
Coordination number $= 3 \times 2 = 6$
(Charge check: $x + 3(-2) = -4 \Rightarrow x = +2$, so Ni is $Ni^{2+}$.)

Concept Bidentate oxalate ligand

Coordination Compounds in past papers

104 questions from this chapter have appeared across 27 exam years.