What is the oxidation state of copper in the $[Cu(NH_3)_4]^{2+}$ ion?

$A$ coordination compound with the formula $FeCl_3 \cdot 4NH_3$ has a coordination number of $6$ for the central metal ion. It does not lose $NH_3$ gas upon heating but gives a white precipitate with an aqueous solution of $AgNO_3$. What is the $IUPAC$ name of this complex?

The $IUPAC$ name of $Na_{3}[Co(NO_{2})_{6}]$ is

The $IUPAC$ name of $[Co(NH_3)_6]Cl_3$ is

In which of the following coordination compounds is the central metal ion in the zero oxidation state?

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