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EEJ MAIN Chemistry QUESTION #5548
Question 1
Arrange the ionic radii of $N^{3-}$, $O^{2-}$, and $F^-$ in correct increasing order (in Å):
  • 1.36, 1.40 and 1.71 respectively
  • 1.36, 1.71 and 1.40 respectively
  • 1.71, 1.40 and 1.36 respectively✔️
  • 1.71, 1.36 and 1.40 respectively
Correct Answer Explanation
All three ions are isoelectronic (10 electrons each). As nuclear charge increases ($N(7) < O(8) < F(9)$), the electrons are pulled closer, so ionic radius decreases. Therefore: $r(N^{3-}) > r(O^{2-}) > r(F^-)$, i.e., 1.71 Å > 1.40 Å > 1.36 Å.