$(a)$ Answer the following questions :

$(i)$ Which element of the first transition series has highest second ionisation enthalpy ?

$(ii)$ Which element of the first transition series has highest third ionisation enthalpy ?

$(iii)$ Which element of the first transition series has lowest enthalpy of atomisation ?

$(b)$ Identify the metal and justify your answer.

$(i)$ Carbonyl $M(CO)_5$  $(ii)$  $MO_3F$

$(a)$ $(i)$ $\mathrm{Cu} .$ In $\mathrm{Cu}$ the second electron is to be removed from $3 d^{10}$ configuration which is highly stable.

$(ii)$ $\mathrm{Zn}$. The third electron is to be removed from $d^{10}$ configuration which is highly stable.

$(iii)$ $Zn$. Zinc has all electrons paired and hence it cannot form metallic bonds.

(b) (i) $\mathrm{Fe}(\mathrm{CO})_{5}$ As per Effective Atomic Number (EAN) rule.

EAN $=Z$ - [Number of electrons lost to form metalion] + [Number of electrons gained from donor atom]

$\therefore$ EAN $=26-0+(5 \times 2)=36$

$(ii)$ $\mathrm{MnO}_{3} \mathrm{~F}: \mathrm{Mn}$ shows $(+7)$ oxidation state.