The first ionization energy of magnesium is smaller as compared to that of
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 :

1. chlorine, lithium and sodium

2. argon, lithium and sodium

3. argon, chlorine and sodium

4. neon, sodium and chlorine

Correct Option: , 3

Solution:

The $1^{\text {st }}$ IE order of $3^{\text {rd }}$ period is

$\mathrm{Na}<\mathrm{Al}<\mathrm{Mg}<\mathrm{Si}<\mathrm{S}<\mathrm{P}<\mathrm{Cl}<\mathrm{Ar}$

$X \& Y$ are $A r \& C l$

$\mathrm{Z}$ is sodium $(\mathrm{Na})$.