What is the value of the effective atomic number $(EAN)$ of cobalt in the $[Co(NH_3)_6]^{3+}$ complex,given that the atomic number of $Co$ is $Z=27$?

What is the Effective Atomic Number $(EAN)$ of $Co$ in $[Co(NH_3)_6]^{3+}$?

The $EAN$ of $Mg$ in $[Mg(EDTA)]^{2-}$ is ...

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

$a$. 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 $EAN$ of metal atoms in $Fe(NO)_2(CO)_2$ and $Co_2(CO)_8$ respectively are