The oxidation state of nickel in the complex $K_4[Ni(CN)_4]$ is .......

The $IUPAC$ name of $[Cr(en)_3]Cl_3$ is

The $IUPAC$ name of $[Co(NH_3)_4 Cl(NO_2)] Cl$ is

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 for $[Co(NH_3)_6] [Cr(CN)_6]$ is:

The charge on cobalt in $[Co(CN)_6]^{3-}$ is