Oxidation number of $Cr$ in $[Cr(CO)_6]$ is

In which of the following complexes is the nickel metal in the highest oxidation state?

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

Specify the oxidation numbers of the metals in the following coordination entities:
$(i) [Co(H_{2}O)(CN)(en)_{2}]^{2+}$
$(ii) [CoBr_{2}(en)_{2}]^{+}$
$(iii) [PtCl_{4}]^{2-}$
$(iv) K_{3}[Fe(CN)_{6}]$
$(v) [Cr(NH_{3})_{3}Cl_{3}]$

The $IUPAC$ name of the complex $\left[Pt\left(NH_{3}\right)_{2} Cl\left(NH_{2} CH_{3}\right)\right] Cl$ is:

Which formula and its name combination is incorrect?