The chemistry of lithium is very similar to that of magnesium even though they are placed in different groups. Its reason is

From the given set of species, point out the species from each set having least atomic radius:-

$\left(\mathrm{i}\right) {\mathrm{O}}^{-2},{\mathrm{F}}^{-},{\mathrm{Na}}^{+}$

$\left(\mathrm{ii}\right) \mathrm{Ni},\mathrm{Cu},\mathrm{Zn}$

$\left(\mathrm{iii}\right) \mathrm{Li}, \mathrm{Be}, \mathrm{Mg}$

$\left(\mathrm{iv}\right) \mathrm{He},{\mathrm{Li}}^{+},{\mathrm{H}}^{-}$

$\mathrm{Be}$ and $\mathrm{Mg}$ have zero value of electron affinity, because:

In the following electronic configuration:

${\mathrm{ns}}^2\left(\mathrm{n}-1\right){\mathrm{d}}^{0-1}\left(\mathrm{n}-2\right){\mathrm{f}}^{1-14}$ If value of $\left(\mathrm{n}-1\right)=6$ the configuration will be of: