In case of isoelectronic species the size of F⁻, Ne and Na⁺is affected by :

Solution

Chemistry ma’am · 3 steps

Same 10 electrons, same shell; only the proton count changes, so the nuclear pull decides the size.

1. What is common. F⁻, Ne and Na⁺ each have 10 electrons in the same arrangement, 1s² 2s² 2p⁶. So the outermost shell is n = 2 for all three.

   Species	Nuclear charge Z	Electrons	Outermost shell
   F⁻	9	10	n = 2
   Ne	10	10	n = 2
   Na⁺	11	10	n = 2

2. What changes. Only the nuclear charge changes, from 9 to 11. With the same 10 electrons and the same shielding, more protons pull the electron cloud in harder, so the size shrinks as Z rises.
3. So. The sizes follow F⁻ > Na⁺, and the factor that sets them is the nuclear charge (Z), option (a).

The idea to keep. For isoelectronic species, line them up by Z: more protons pulling on the same set of electrons means a smaller particle.

Answer from the NTA final answer key. Solution by PrepWiser.