Question

Which ion has the smallest ionic radius?

• A. ${Li}^{+}$
• B. $B^{3+}$
• C. $N^{3-}$
• D. $O^{2-}$

Answer 1

The correct option is B $B^{3+}$

${Li}^{+}$ & $B^{3+}$ are isoelectronic with $He$ and $N^{3-}$ and $O^{2-}$ are iso electronic with $Ne$. $He$ is smaller than $Ne$. Hence ${Li}^{+},B^{3+}$ are smaller than $N^{3-}$ and $O^{2-}$. Among ${Li}^{+}$ & $B^{3+}$, $B^{3+}$ is smaller as it has higher nuclear charge due to which its size is reduce as electrons are strongly attracted. Hence among given options, $B^{3+}$ is smallest.