Question

Which one of the following ions has the highest value of ionic radius?

• A. $L{i}^{+}$
• B. $B^{3+}$
• C. $O^{2-}$
• D. $F^{-}$

Answer 1

The correct option is C $O^{2-}$

This can be explained on the basis of $z/e\left\{\frac{\text{nuclear charge}}{\text{no. of electrons}}\right\}$, as z/e ratio increases, the size decreases and when z/e ratio decreases the size increases.
For $L{i}^{+},\frac{z}{e}=\frac{3}{2}=1.5$
For $B^{3+},\frac{z}{e}=\frac{5}{2}=2.5$
For $O^{2-},\frac{z}{e}=\frac{8}{10}=0.8$
For $F^{-},\frac{z}{e}=\frac{9}{10}=0.9$
Hence, $O^{2-}$ has highest value of ionic radius.