Chemistry - PERIODIC TABLE Question with Solution | TestHub

Ionisation energy decreases with increase in the size of atom. $\mathrm{Na}, \mathrm{K}, \mathrm{Rb}$ belongs to alkali metal and down the group ionization energy decreases as size of atom increases down the group.  Among the given elements, $\mathrm{Sc}$ being small has the highest ionization energy $(\mathrm{Na}= 496, \mathrm{K}=419; \mathrm{Sc} =631 \mathrm{kJ} {\mathrm{mol}}^{-1})$