Question

Which of the following is the largest is size?

• A. $Cl^{-}$
• B. $S^{2-}$
• C. $Na^{+}$
• D. $F^{-}$

Answer 1

Answer: (B)

$S^{2-}$

Answer 2

$C l^{-}$and $S^{2-}$ are isoelectronic species (containing equal number of electrons, i.e., $18$). Their radii would be different because of their different nuclear charge. Anion with the greater negative charge will have the larger radius hence $S^{2-}$ has larger size than $C l^{-}$. For isoelectronic species, radii $\propto \frac{1}{Z}$ Further $Na ^{+}$and $F ^{-}$ are also isoelectronic species but they have $10$ electrons. Hence, their sizes are smaller than $S ^{2-}$ ion.