JEE Main · 2016 · 03 Apr 2016 · Offline · Classification of Elements and Periodicity

Which of the following atoms has the highest first ionization energy?

(A)Na
(B)K
(C)Sc✓ Correct
(D)Rb

Answer: (C)

Solution

Down a group, ionisation energy falls, so among the alkali metals sodium is higher than potassium, which is higher than rubidium. Scandium, though, is a fourth-period transition metal with a smaller radius and a larger effective nuclear charge than sodium, so it grips its outer electron more tightly still. The highest first ionisation energy of the four is scandium's.

JEE Main · 2016 · 03 Apr 2016 · Offline · Single correct option

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