Question:
The first ionization energy of magnesium is smaller as compared to that of elements $\mathrm{X}$ and $\mathrm{Y}$, but higher than that of $Z$. the elements $X, Y$ and $Z$, respectively, are:
Correct Option: , 3
Solution:
The $1^{\text {st }}$ IE order of $3^{\text {rd }}$ period is
$\mathrm{Na}<\mathrm{Al}<\mathrm{Mg}<\mathrm{Si}<\mathrm{S}<\mathrm{P}<\mathrm{Cl}<\mathrm{Ar}$
$\mathrm{X} \& \mathrm{Y}$ are $\mathrm{Ar} \& \mathrm{Cl}$
$Z$ is sodium (Na).