(i.e $en$ and $C_2O_4$ ), so coordination number of $E$ is $6$

                        $(2 \times 2 + 1 \times 2 = 6)$

Let the oxidation state of $E$ in complex be $x$, then

$[x + (-2) = 1]$ or $x -2 = 1$

or $x = + 3$, so its oxidation state is $+ 3$ Thus option $(d)$ is correct.