Question

The ionic radii of $F^{-}$ and $O^{2-}$ respectively are $1.33\stackrel{\circ }{A}$ and $1.4\stackrel{\circ }{A}$ while the covalent radius of $N$ is $0.74\stackrel{\circ }{A}$.

The correct statement for the ionic radius of $N^{3-}$ from the following is :

• A. It is smaller than $O^{2-}$ and $F^{-}$ , but bigger than of $N$
• B. It is bigger than $F^{-}$ and $N$, but smaller than of $O^{2-}$
• C. It is bigger than $O^{2-}$ and $F^{-}$
• D. It is smaller than $F^{-}$ and $N$

Answer 1

The correct option is C It is bigger than $O^{2-}$ and $F^{-}$

For isoelectronic species, as the charge on anion increases, the ionic radius increases $F^{-},O^{2-}$ and $N^{3-}$ has $10$ electrons each. The decreasing order of their ionic radii is
$N^{3-}>O^{2-}>F^{-}$
Now, Anions have more ionic radii than corresponding neutral atom thus anion $N^{3-}$ will have more ionic radii than covalent radii of $N$.
$\therefore N^{3-}$ is bigger than both $O^{2-}$ and $F^{-}$
Correct option is C.