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

The size of isoelectronic species; ${\mathrm{F}}^{-},\mathrm{Ne}\text{ and }{\mathrm{Na}}^{+}$ is affected by nuclear charge (Z). With increase in nuclear charge (atomic number), the size of the isoelectronic species decreases.