Question

The ionic radii of N^3-, O^2-, F^- and Na⁺ follow the order:

• A. N^3- > O^2- > F^- > Na⁺
• B. N^3- > Na⁺ > O^2- > F^-
• C. Na⁺ > O^2- > N^3- > F^-
• D. O^2- > F^- > Na⁺ > N^3-

Hint:

These four ions are isoelectronic; more protons means smaller size.

Answer 1

The Correct Option is A

Step 1: N^3-, O^2-, F^- and Na⁺ are all isoelectronic species. Each one has 10 electrons, the same electronic configuration as neon.

Step 2: For isoelectronic species, the electron count is fixed, so the size depends only on the nuclear charge. A higher nuclear charge pulls the same 10 electrons in more strongly, shrinking the radius.

Step 3: The atomic numbers are N = 7, O = 8, F = 9, Na = 11. So the pull on the electron cloud increases in this order: N < O < F < Na.

Step 4: More pull means a smaller radius, so the radius decreases in the same order. It is largest for N^3- and smallest for Na⁺.

Step 5: So the order of radii is N^3- > O^2- > F^- > Na⁺, matching option A.