In the coordination compound $K_4[Ni(CN)_4]$,the oxidation state of nickel is:

The oxidation number of the central metal in $[Pt(NH_3)_2Cl(NO_2)]$ and $[CoCl_2(en)_2]^{\oplus}$,respectively,are

State the $IUPAC$ name of the following complex: $[Cr(C_2O_4)_3]^{3-}$

The oxidation number of iron in the compound $K_4[Fe(CN)_6]$ is

Write the formulas for the following coordination compounds:
$(a)$ Tetraammineaquachloridocobalt $(III)$ chloride
$(b)$ Potassium tetrahydroxidozincate $(II)$
$(c)$ Potassium trioxalatoaluminate $(III)$
$(d)$ Dichloridobis(ethane$-1,2-$diamine)cobalt $(III)$
$(e)$ Tetracarbonylnickel $(0)$

Which formula and name combination is incorrect?