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

Pick out the complex compound in which the central metal atom obeys the $EAN$ rule strictly.

What is the effective atomic number $(EAN)$ of $Fe$ in $[Fe(CN)_6]^{4-}$? (Atomic number of $Fe = 26$)

Which of the following complexes does the central metal ion $NOT$ obey the $EAN$ rule? (Atomic numbers: $Pt=78, Cu=29, Zn=30, Fe=26$)

$a$. 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 $M(CO)_5$
$ii$. $MO_3F$

The effective atomic number $(EAN)$ of $Co(CO)_4$ is $35$ and hence it is less stable. It attains stability by