inversely proportional to effective nuclear charge
inversely proportional to square of effective nuclear charge
directly proportional to effective nuclear charge
directly proportional to square of effective nuclear charge
Solution
Ionic radius in the $n^{\text {th }}$ orbit is given by
$r_n=\frac{n^2 a_0}{\mathrm{Z}} \text { or, } r_n \propto \frac{1}{\mathrm{Z}}$
Related Theory
The radius of the ion depends on the effective nuclear charge, more the charge, more heavily the electrons are attracted towards the centre and lesser in the size.