Question:

The ionic radii of \(\mathrm{F^-}\) and \(\mathrm{O^{2-}}\) respectively are \(1.33\ \mathrm{\AA}\) and \(1.4\ \mathrm{\AA}\), while the covalent radius of N is \(0.74\ \mathrm{\AA}\).

The correct statement for the ionic radius of \(\mathrm{N^{3-}}\) from the following is :

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N3-, O2- and F- are isoelectronic; among isoelectronic ions the one with the smallest nuclear charge has the largest radius. An anion is also larger than its parent atom.
Updated On: Nov 4, 2026
  • It is smaller than \(\mathrm{F^-}\) and N
  • It is bigger than \(\mathrm{O^{2-}}\) and \(\mathrm{F^-}\)
  • It is bigger than \(\mathrm{F^-}\) and N, but smaller than of \(\mathrm{O^{2-}}\)
  • It is smaller than \(\mathrm{O^{2-}}\) and \(\mathrm{F^-}\), but bigger than of N
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The Correct Option is B

Solution and Explanation

\(\mathrm{N^{3-}}\), \(\mathrm{O^{2-}}\) and \(\mathrm{F^-}\) are isoelectronic (10 electrons) with nuclear charges 7, 8 and 9.
For isoelectronic species, radius decreases as nuclear charge increases: \(\mathrm{N^{3-} \gt O^{2-} \gt F^-}\).
Also, an anion is larger than its neutral atom, so \(\mathrm{N^{3-}}\) is bigger than N (0.74 \(\mathrm{\AA}\)); its actual ionic radius is about 1.71 \(\mathrm{\AA}\).
So \(\mathrm{N^{3-}}\) is bigger than both \(\mathrm{O^{2-}}\) and \(\mathrm{F^-}\).
Answer: (2) It is bigger than \(\mathrm{O^{2-}}\) and \(\mathrm{F^-}\)
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