IUPAC name of coordination compound $K_3[Fe(CN)_6]$ is

Question

$\begin{array}{1 1}(a)\;Potassium\;hexa\;cyanoferrate(II)\\(b)\;Potassium\;hexa\;cyano\;ferrate(III)\\(c)\;Potassium\;hexa\;cyanoiron(III)\\(d)\;Potassium\;hexa\;cyanoiron(II)\end{array}$