In the isoelectronic species the ionic radii (A^o) of N^3–, O^2–, F^– are respectively given by

In case of isoelectronic species, Ionic radius increases as -ve charge(no. of electrons) increases and +ve charge(nuclear charge) decreases.

Hence Ionoic radii of N^3–, O^2–, F^– are 1.71, 1.40, 1.36 respectively.