Question

The radii of $F,F^{-},O^{-}$ and $O^{2-}$ are in the order:

• A. $O^{2-}>O^{-}>F^{-}>F$
• B. $O^{2-}>F>F^{-}>O^{-}$
• C. $F^{-}>O^{2-}>F>O^{-}$
• D. $O^{2-}>O^{-}>F>F^{-}$

Answer 1

The correct option is A $O^{2-}>O^{-}>F^{-}>F$

$O^{2-}$ & $F^{-}$ are isoelectronic and $O^{-}$ and $F$ are isoelectronic. For isoelectronic species, the element of the higher atomic number is smaller. Also for ions of the same element, more negative ions are bigger. Both trends are because of effective nuclear charge.

Thus the conclusions are $O^{2-}>O^{-};F^{-}>F,O^{-}>F,O^{2-}>F^{-}$. Thus final correct order is $O^{2-}>O^{-}>F^{-}>F$