Question

Find the oxidation number of Fe in $\left[Fe\right(CN{)}_6{]}^{4-}$.

Answer 1

Let X be the oxidation number of Fe in $\left[Fe\right(CN{)}_6{]}^{4-}$.
The oxidation number of cyano group is -1.
$=X+6(-1)=-4$
$=X-6=-4$
$=X=6-4$

$X=+2$

The oxidation number of Fe in $\left[Fe\right(CN{)}_6{]}^{4-}$ is $+2$.