Increasing order of ionic radii of the followings:
(A) $Eu^{3+}$
(B) $Lu^{3+}$
(C) $Y^{3+}$
(D) $La^{3+}$
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (B) < (C) < (A) < (D)
The increasing order of ionic radii is - Lu³⁺ < Y³⁺ < Eu³⁺ < La³⁺.
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Lanthanide contraction:
In the lanthanide series, the ionic radius decreases from La³⁺ to Lu³⁺ because the 4f electrons do not shield the nuclear charge effectively, causing a stronger attraction between the nucleus and electrons. -
Therefore:
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Lu³⁺ (last lanthanide) has the smallest radius.
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Eu³⁺ is larger than Lu³⁺ but smaller than La³⁺.
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La³⁺ (first lanthanide) has the largest radius among the lanthanides listed.
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Y³⁺ comparison:
Y³⁺ has a radius slightly larger than Lu³⁺ but smaller than Eu³⁺, because its size is comparable to the heavier lanthanides due to lanthanide contraction.
Thus the increasing order becomes:
Lu³⁺ < Y³⁺ < Eu³⁺ < La³⁺
or
(B) < (C) < (A) < (D).