Question

The first ionization energy of magnesium is smaller as compared to that of elements X and Y but higher than that of Z. The elements X, Y and Z, respectively are:

• A. argon, lithium and sodium
• B. chlorine, lithium and sodium
• C. neon, sodium and chlorine
• D. argon, chlorine and sodium

Answer 1

The correct option is D argon, chlorine and sodium

Order of Ionisation energy across the period increases due to increase in nuclear charge.

3rd period → $Na<Al<Mg<Si<S<P<Cl<Ar$

Hence, chlorine and argon will have higher first ionisation energy than magnesium.
Sodium and lithium will have less first ionisation energy than magnesium because removing an electron will give a stable electronic configuration from them.
Hence, option (d) is correct.