JEE Main · 2008 · 27 Apr 2008 · Offline · Coordination Compounds

Ethylenediamine is a bidentate ligand and two of them occupy four coordination sites, while the oxalate ion is also bidentate and occupies two more, so the central element $E$ is surrounded by six donor atoms and its coordination number is six. For the oxidation state, the nitrite ion sits outside the coordination sphere as $\mathrm{N}{\mathrm{O}}_2^{-}$, so the complex ion carries a single positive charge; with two neutral $\mathrm{en}$ ligands and an oxalate of charge $-2$, the balance $x+(-2)=+1$ fixes the oxidation state of $E$ at $+3$. So the coordination number is six and the oxidation state is three.