Q. The correct order of ionic radii of $Y^{3 +},\ {La}^{3 +},\ {Eu}^{3 +}\ and\ {Lu}^{3 +}$ is
A) $Y^{3 +} <$ ${La}^{3 +} <$ ${Eu}^{3 +} <$ ${Lu}^{3 +}$
B) ${Lu}^{3 +} <$ ${Eu}^{3 +} <$ ${La}^{3 +}$ ${< Y}^{3 +}$
C) ${La}^{3 +} < {Eu}^{3 +} <$ ${Lu}^{3 +}$ $< Y^{3 +}$
D) $Y^{3 +} <$ ${Lu}^{3 +} <$ ${Eu}^{3 +} < {La}^{3 +}$
Explanation
(d)
Ionic radii of lanthanide$(La^{3 +})$ decreases with increase in atomic numbe.
$Y^{3 +} <$ ${Lu}^{3 +} <$ ${Eu}^{3 +} < {La}^{3 +}$
Because $Eu$ and $Lu$ are the members of lanthanide series (so they show lanthanide contraction) and La is the representative element. $Y^{3 +}$ ion has lower ionic radii as comparison to ${La}^{3 +}$ because it lies immediately above in Periodic Table.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.