The size of isoelectronic species $-\mathrm{F}^{-}, \mathrm{Ne}$ and $\mathrm{Na}^{+}$is affected by
(a) Nuclear charge (Z )
(b) Valence principal quantum number (n)
(c) Electron-electron interaction in the outer orbitals
(d) None of the factors because their size is the same.
The size of an isoelectronic species increases with a decrease in the nuclear charge (Z). For example, the order of the increasing nuclear charge of F–, Ne, and Na+ is as follows:
$\mathrm{F}^{-}<\mathrm{Ne}<\mathrm{Na}^{+}$
Z 9 10 11
Therefore, the order of the increasing size of $\mathrm{F}^{-}, \mathrm{Ne}$ and $\mathrm{Na}^{+}$is as follows:
$\mathrm{Na}^{+}<\mathrm{Ne}<\mathrm{F}^{-}$
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