d
d
\(\mathrm{en},\)  \(\begin{array}{*{20}{c}}  {C{H_2} - N{H_2}} \\   {|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \\   {C{H_2} - N{H_2}} \end{array}\)  is bidentate ligand
\(\mathrm{C}_{2} \mathrm{O}_{4}^{2-}\) is also bidentate ligand. Hence, coordination number of the element \(E\) in the given complete comes out to be \(6 .\) The complex can be ionised as

\(\left[E(e n)_{2}\left(C_{2} O_{4}\right)\right] N O_{2} \longrightarrow\) \(\left[E(e n)_{2}\left(C_{2} O_{4}\right)\right]^{+} N O_{2}^{-}\)

Oxidation number \(x+0+(-2)=+1\)

\(\Rightarrow\) Oxidation number, \(x=3\)