The oxidation number of iron in potassium ferrocyanide is

The $IUPAC$ name of the red coloured complex $[Fe(C_4H_7O_2N_2)_2]$ obtained from the reaction of $Fe^{2+}$ and dimethyl glyoxime is:

In which of the following compounds does the transition metal have a zero oxidation state?

In which of the following complexes is the oxidation state of the metal zero?

The oxidation states of iron atoms in compounds $(A),$ $(B)$ and $(C),$ respectively,are $x,$ $y$ and $z.$ The sum of $x, y$ and $z$ is........
$(A)$ $Na_4[Fe(CN)_5(NOS)]$
$(B)$ $Na_4[FeO_4]$
$(C)$ $[Fe_2(CO)_9]$

The $IUPAC$ name of $K_2[OsCl_5N]$ is: