• # question_answer The radii of $F,\,{{F}^{-}},\,O$ and ${{O}^{-2}}$ are in the order of [AIIMS 1999; CPMT 1999] A) ${{O}^{2-}}>{{F}^{-}}>O>F$ B) ${{O}^{2-}}>{{F}^{-}}>F>O$ C) ${{F}^{-}}>{{O}^{2-}}>F>O$ D) ${{O}^{2-}}>O>{{F}^{-}}>F$

Atomic radius decreases on going from left to right in a period. Thus size of $O>F$. As ${{O}^{2-}}$ and ${{F}^{-}}$are isoelectronic, therefore, size of ${{O}^{2-}}>{{F}^{-}}.$