The correct graph between the gravitational potential $\left({\mathrm{V}}_g\right)$ due to a hollow sphere and distance from its centre will be

Inside the sphere, V is constant and is equal to that on the surface of the sphere. Outside the sphere it comes out to be, V=-Gm/r i.e. $\left|\mathrm{V}\right|\propto 1/\mathrm{r}$. Hence the graph (c) is correct.