Question

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

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

Answer 1

Answer: (A)

${{O}^{2-}}>{{F}^{-}}>O>F$

Answer 2

Note: In a period from left to right, as the atomic number increases, atomic radii decreases. Therefore, in F and O, oxygen has higher value of atomic radii than fluorine. $\text{Radii}\propto \frac{\text{1}}{\text{Effective}\,\text{nuclear}\,\text{charge}}$ Hence, anions have bigger size than parent atom as the effective nuclear charge decrease by increasing the -ve charge. So, ${{\text{O}}^{2-}}$ has greater size than ${{\text{F}}^{-}}$ Thus, the correct order is: ${{O}^{2-}}O>F$