i. The radii of isoelectronic species vary according to actual nuclear charge. Larger nuclear charge exerts greater attraction on the electrons and thus, the radius of that isoelectronic species becomes smaller.
ii. For example, F- and Na+ both have 10 electrons but the nuclear charge on F- is +9 which is smaller than that of Na+ which has the nuclear charge +11.
Hence, F has larger ionic radii (133 pm) than Na+ (98 pm).
