The size of isoelectronic species-${\mathrm{F}}^{-}, {\mathrm{Na}}^{+}$ and Mg²⁺ is affected by :

The correct option is A)

As the atomic radius increases, the nuclear charge decreases, and the electrons will become more loosely bound.

Atomic radius $\propto$$\frac{1}{\mathrm{Nuclear} \mathrm{charge} }$

Order size is ${\mathrm{Mg}}^{2+}<{\mathrm{Na}}^{+}<{\mathrm{F}}^{-}$.