Question

The correct order of ionic radii of $Y ^{3+}, La ^{3+}$ $Eu ^{3+}$, and $Lu ^{3+}$ is : -
(Atomic nos. $Y =39,\, La =57,\, Eu =63,\, Lu =71$.)

• A. $Lu^{3+ } < Eu^{3+} < La^{3+} < Y^{3+} $
• B. $La^{3+ } < Eu^{3+} < Lu^{3+} < Y^{3+} $
• C. $Y^{3+ } < La^{3+} < Eu^{3+} < Lu^{3+} $
• D. $Y^{3+ } < Lu^{3+} < Eu^{3+} < La^{3+} $

Answer 1

Answer: (D)

The correct order of ionic radii of $Y^{3+},La^{3+},Eu^{3+} $ and $ Lu^{3+}, $ is $Y^{3+} < Lu^{3+} < Eu^{3+} < La^{3+} $ because Eu and Lu are the members of lanthanide series (so they show lanthanide contraction) and La is the representative element of all elements of such series and $Y^{3+} $ ion has lowei radii as comparison to $La^{3+} $ because it lies immediately above it in the periodic table.