Question

The correct order of ionic radii of $Ce$, $La$, $Pm$ and $Yb$ in $+3$ oxidation state is

• A. $La^{3+} < Pm^{3+} < Ce^{3+} < Yb^{3+} $
• B. $Yb^{3+} < Pm^{3+} < Ce^{3+} < La^{3+} $
• C. $La^{3+} < Ce^{3+} < Pm^{3+} < Yb^{3+} $
• D. $Yb^{3+} < Ce^{3+} < Pm^{3+} < La^{3+} $

Answer 1

Answer: (B)

The overall decrease in atomic and ionic radii from $La^{3+}$ to $Lu^{3+}$ is called lanthanoid contraction. Hence, the correct order is $Yb^{3+} < Pm^{3+} < Ce^{3+} < La^{3+}$