JEE Main · 2019 · 09 Apr 2019 · Shift 1 · Classification of Elements and Periodicity

The element having greatest difference between its first and second ionization energies, is

(A)Ca
(B)K✓ Correct
(C)Ba
(D)Sc

Answer: (B)

Solution

The widest gap between the first and second ionisation energies belongs to potassium. Its single

4 s

electron comes off easily to leave the argon core, but the second electron must then be torn out of that closed noble-gas shell, which costs far more. Calcium, barium and scandium each still have an accessible second electron in the same outer region, so their jump is gentler.

JEE Main · 2019 · 09 Apr 2019 · Shift 1 · Single correct option

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