Identify the elements X and Y using the ionisation energy values given below :

$\mathrm{Na} \rightarrow[\mathrm{Ne}] 3 \mathrm{~s}^{1} \mathrm{IE}_{1}$ is very low but $\mathrm{IE}_{2}$ is very high due to stable noble gas configuration of

$\mathrm{Na}^{+}$

$\mathrm{Mg} \rightarrow[\mathrm{Ne}] 3 \mathrm{~s}^{2} \mathrm{IE}_{1} \& \mathrm{IE}_{2} \rightarrow$ Low

$\mathrm{IE}_{3}$ is very high.