Question

The correct increasing order of first ionisation energy is:

• A. Na < K < Al < Mg
• B. K < Na < Al < Mg
• C. K < Na < Mg < Al
• D. K < Mg < Al < Na.

Answer 1

The correct option is B

K < Na < Al < Mg

Ionisation energy decreases down the group, but increases from left to right in a period. So, K < Na < Al < Mg is the correct order of ionization energy.

Potassium is present in the fourth period. Sodium, aluminium and magnesium are present in the third period.