Classification of Elements Part 1

The order of first ionisation energy of 3‌nd ‌ period is as follows
On moving along a period from left to right, nuclear charge increases that outweighs the shielding effect. As a result, outermost electrons are held more tightly. Hence, ionisation enthalpy increases.
Ionisation enthalpy of group 2 is greater than group 13 and that of group 15 is greater than group 16. This is due to fully filled and half-filled orbital.
∴X,Y and Z are argon, chlorine and sodium respectively.