Question

Which of the following isoelectronic species has the largest size?

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

Answer 1

Answer: (C)

All the ions are isoelectronic but they have different size due ot different values of $Z$. In $Na ^{+}, O ^{2-}, N ^{3-}, F ^{-}$, number of electrons are 10 but, $r \propto \frac{1}{Z}$. Thus greater the value of $\frac{e}{Z}$ greater the size of iso-electronic species. Hence $N ^{3-}$ is largest in size.