Question

When the ionisation energy v/s atomic number is plotted for the elements, of atomic number $11$ to $18$, two peaks are observed for the elements $X$ and $Y$ in between the curve. What is the difference between an atomic number of an element $X$ and element $Y$?

Answer 1

Ionization energy v/s Atomic number curve.

for element 11 to 18 is :-

Atomic Number $\to$ Peak is observed at Mg (At. No = 12) and

P (At. No = 15).

It is because 'Mg' has completely filled orbitals and 'P' has half filled orbitals.

Difference between Atomic number of x and y is $|12-15|=\left|3\right|$