The curve for the moment of inertia of a sphere of constant mass M versus its radius of gyration K will be

The moment of inertia of a sphere is given by
$\mathrm{I}=\frac{2}{5}{\mathrm{MK}}^2\text{ or }\mathrm{I}\propto {\mathrm{K}}^2$
This is an equation of parabola passing through origin