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

Identify true and false statements:
$(a)$ In the reaction $F_2 + O_2 \to O_2F_2$,oxygen is an oxidising agent.
$(b)$ Among $HClO, HClO_2, HClO_3$ and $HClO_4$,$HClO_2$ is the strongest acid.
$(c)$ Oxidation state of Nickel in $[Ni(CO)_4]$ is zero.
$(d)$ The reaction $BaO_2 + H_2SO_4 \to BaSO_4 + H_2O_2$ is a redox reaction.
The correct order of truth values is:

The oxidation number and coordination number of cobalt in $K[Co(CO)_4]$ are

The brown ring complex compound is $[Fe(H_2O)_5(NO)]SO_4$. What is the oxidation state of iron in this complex?

$Pt + 3:1$ mixture of (conc. $HCl +$ conc. $HNO_3$) $\rightarrow [X]^{2-}$. What is the oxidation state of $Pt$ in $[X]^{2-}$ complex ion?

According to $IUPAC$ nomenclature,the correct name of the compound $[Cu(NH_3)_4](NO_3)_2$ is: