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

(A) . $i$. $Cu$. In $Cu$,the second electron is removed from a $3d^{10}$ configuration,which is highly stable.
$ii$. $Zn$. The third electron is removed from a $d^{10}$ configuration,which is highly stable.
$iii$. $Zn$. Zinc has all electrons paired and hence it cannot form strong metallic bonds.
$b$. $i$. $Fe(CO)_5$. According to the Effective Atomic Number $(EAN)$ rule,$EAN = Z - \text{electrons lost} + \text{electrons gained}$.
$EAN = 26 - 0 + (5 \times 2) = 36$.
$ii$. $MnO_3F$. $Mn$ shows a $(+7)$ oxidation state.