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

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

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

During the race of complex compounds,the finish line is fixed by achieving an $E.A.N.$ value equal to the atomic number of the corresponding inert gas. Which of the following complexes is present at the finish line?

The effective atomic number $(EAN)$ of $Co(CO)_4$ is $35$,which makes it less stable. It attains stability by:

The effective atomic number of Iron $(Z = 26)$ in $[Fe(CN)_6]^{3-}$ is