What is the oxidation number of $Pt$ in $[PtCl_6]^{2-}$?

$IUPAC$ name of $H_2[PtCl_6]$ is

Write the formulas for the following coordination compounds:
$(i)$ Tetraamminediaquacobalt$(III)$ chloride
$(ii)$ Potassium tetracyanidonickelate$(II)$
$(iii)$ Tris(ethane$-1,2-$diamine)chromium$(III)$ chloride
$(iv)$ Amminebromidochloridonitrito$-N-$platinate$(II)$
$(v)$ Dichloridobis(ethane$-1,2-$diamine)platinum$(IV)$ nitrate
$(vi)$ Iron$(III)$ hexacyanidoferrate$(II)$

State the $IUPAC$ name of the following complex: $[Co(en)_{2}(ONO)Cl]Cl$

What is the $IUPAC$ name of the coordination compound $[Co(NH_3)_3(NO_2)(Cl)(CN)]$?

The correct $IUPAC$ name of $cis-$platin is