The ionic radii (in $\AA$) of $\mathrm{N}^{3-}$, $\mathrm{O}^{2-}$ and $\mathrm{F}^{-}$ are respectively:

JEE Main · 2015 · 04 Apr 2015 · Offline · Classification of Elements and Periodicity

The ionic radii (in

\overset{˚}{A}

) of

N^{3 -}

O^{2 -}

and

F^{-}

are respectively:

Answer: (B)

These three ions are isoelectronic -- each has

10

electrons -- so their size is decided by nuclear pull alone. Going

N^{3 -} (7 p) \to O^{2 -} (8 p) \to F^{-} (9 p)

, the growing nuclear charge draws the same electron cloud inward, so the radii shrink in that order. That matches

1.71

for

N^{3 -}

1.40

for

O^{2 -}

and

1.36

Angstrom for

F^{-}

JEE Main · 2015 · 04 Apr 2015 · Offline · Single correct option