Periodic Table

Step 1: Concept of isoelectronic species.
Na , Mg , Al , and F are isoelectronic (each has 10 electrons). The ionic size depends mainly on the nuclear charge (Z).
Step 2: Effect of nuclear charge.
As nuclear charge increases, the same number of electrons are pulled more strongly toward the nucleus, decreasing the ionic radius.
Step 3: Order of Z (atomic number).
F (9) Hence, radius order (inverse relation): Step 4: Conclusion.
The correct order of ionic radii is F >Na >Mg >Al .