$(a)$ 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.
Which of the following transitional metal has lowest density
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Correct statement for $3d-$ series is