Q. What is the correct decreasing order of ionic radii of following ions? $N^{3 -},O^{2 -},\ F^{-},Na^{+},Mg^{2 +}$
A) $N^{3 -} > O^{2 -} > F^{-} > Mg^{2 +} > Na^{+}$
B) $N^{3 -} > O^{2 -} > F^{-} > Na^{+} > Mg^{2 +}$
C) $N^{3 -} > O^{2 -} > Mg^{2 +} > Na^{+} > F^{-}$
D) $Na^{+} > F^{-} > O^{2 -} > Mg^{2 +} > N^{3 -}$
Explanation
(b)
Ionic radii $\propto \frac{1}{z_{eff}} \propto$ charge of anion
$\propto \frac{1}{charge\ on\ cation}$
Thus, the order of ionic radii is
$N^{3 -} > O^{2 -} > F^{-} > Na^{+} > Mg^{2 +}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.