Question

In which of the following pairs of species, the size of the first species is not more than the second species?

• A. $N{a}^{+},F^{-}$
• B. $F{e}^{2+},F{e}^{3+}$
• C. $Li,F$
• D. $S,O$

Answer 1

Answer: (A)

$N{a}^{+},F^{-}$

$N{a}^{+}$ and $F^{-}$ are isoelectronic species with 10 electrons each. For isoelectronic species, cation has smaller size than anion. In $N{a}^{+}$, 11 protons attract 10 electrons. In $F^{-}$, 9 protons attract 10 electrons. Hence the attraction between nucleus and valence electrons is more for $N{a}^{+}$ than $F^{-}$.