What is the Effective Atomic Number $(EAN)$ of $Cu$ in $[Cu(NH_3)_4]^{2+}$?

Which of the following pairs of complexes have the same $EAN$ of the central metal atoms/ions?

$EAN$ of the central metal in the complexes $K_2[Ni(CN)_4]$,$[Cu(NH_3)_4]SO_4$ and $K_2[PtCl_6]$ are respectively.

$a$. Answer the following questions:
$i$. Which element of the first transition series has the highest second ionisation enthalpy?
$ii$. Which element of the first transition series has the highest third ionisation enthalpy?
$iii$. Which element of the first transition series has the lowest enthalpy of atomisation?
$b$. Identify the metal and justify your answer:
$i$. Carbonyl $M(CO)_5$
$ii$. $MO_3F$

What is the effective atomic number of cobalt in $[Co(NH_3)_6]^{3+}$ if $Co$ has atomic number $Z=27$?

In the complex $Fe(CO)_x$,the value of $x$ is :