Home Chemistry Classification of Elements and Periodicity Atomic and Ionic Radius The correct order of size of ions Li + , Mg …
Chemistry Classification of Elements and Periodicity Atomic and Ionic Radius Single Correct MCQ
Published on: August 13, 2026

The correct order of size of ions Li + , Mg 2+ , K + , Al 3+ :

A
Al 3+ < Mg 2+ < Li + < K +
B
Mg 2+ < Al 3+ < Li + < K +
C
Al 3+ < Mg 2+ < K + < Li +
D
Al 3+ < Li + < Mg 2+ < K +

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The correct answer is:
A

K + has more number of shells than Mg 2+ and AI 3+ . AI 3+ and Mg 2+ are isoelectronic but AI 3+ has higher nuclear charge, so AI 3+ < Mg 2+ . Mg 2+ and Li + have diagonal relationship. But due to +2 charge in Mg 2+ , the Mg 2+ is smaller than Li + . Hence Al 3+ is the smallest one.

K + = 1.38 Å, Li 2+ = 0.76 Å, Mg 2+ = 0.72 Å and Al 3+ = 0.535 Å.

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