What is the oxidation number of $\mathrm{Fe}$ in $\left[\mathrm{Fe}{\left({\mathrm{H}}_2\mathrm{O}\right)}_5(\mathrm{NO}{]}^{2+}\right.$ ion?

${\mathrm{K}}_3\left[\mathrm{Fe}(\mathrm{CN}{)}_6\right]$ is:

$\left(\mathrm{a}\right)$ Potassium hexacyanoferrate $\left(\mathrm{II}\right)$.
$\left(\mathrm{b}\right)$ Potassium hexacyanoferrate $\left(\mathrm{III}\right)$.
$\left(\mathrm{c}\right)$ Potassium ferri-cyanide
$\left(\mathrm{d}\right)$ Hexacyano ferrate $\left(\mathrm{III}\right)$ potassium.

The correct answer is: