Question

Find the oxidation number of Fe in $N{a}_2\left[Fe\right(CN{)}_{5}NO]$.

Answer 1

Let X be the oxidation number of Fe in $N{a}_2\left[Fe\right(CN{)}_{5}NO]$.
The Na atoms have oxidation number of +1.
The NO group has oxidation number of 0.
The CN group has oxidation number of -1.
$2(+1)+X+5(-1)+0=0$
$2+X-5=0$
$X-3=0$
$X=+3$
The oxidation number of Fe in $N{a}_2\left[Fe\right(CN{)}_{5}NO]$ is $+3$.