Match the following? property metal (a) Element with highest second ionization enthalpy Δ i H 2  …

The atomic number of copper is $29$. It has the electronic configuration of $3{\mathrm{d}}^{10}4{\mathrm{s}}^1$. After the first ionisation energy it has the electronic configuration of $3{\mathrm{d}}^{10}4{\mathrm{s}}^0$. After that it has the very high second ionisation energy because of fully filled $\mathrm{d}-$orbital. Zinc has the atomic number of the $30$. It has the electronic configuration of $3{\mathrm{d}}^{10}4{\mathrm{s}}^2$. After that the second ionisation energy it has the electronic configuration of $3{\mathrm{d}}^{10}4{\mathrm{s}}^0$. After that it has the very high third ionisation energy because of fully filled $\mathrm{d}-$orbital. The carbonyl ligand is two electron donor. The carbonyl ligand follows the eighteen electron rule. So, the electron configuration of metal must be ${\mathrm{d}}^6$. So, this metal is chromium. Hence, $\mathrm{Cr}$ is $\mathrm{M}$ in $\left[\mathrm{M}(\mathrm{CO}{)}_6\right]$. The element with high heat of atomisation is nickel.

Hence, the correct matches are $(\mathrm{a}\to \mathrm{iii}),(\mathrm{b}\to \mathrm{iv}),(\mathrm{c}\to \mathrm{ii}),(\mathrm{d}\to \mathrm{v})$.