The correct order of increasing ionic radii is
 

${\mathrm{N}}^{-3}>{\mathrm{O}}^{-2}>{\mathrm{F}}^{-}>{\mathrm{Na}}^{+}>{\mathrm{Mg}}^{+2}\text{ (Radii) }$
(Isoelectronic species)

In case of Isoelectronic species, 

• As cationic charge increases, size decreases.
• As anionic charge increases, size increases.