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)

$Yb^{3 +} < Pm^{3 +} < Ce^{3 +} < La^{3. +}$

Answer 2

The overall decrease in atomic and ionic radii from $La^{3 +}$ to $Lu^{3 +}$is is isg f is called lanthanoid contraction. Hence the correct order is

$Yb^{3 +} < Pm^{3 +} < Ce^{3 +} < La^{3 +}$