d
The electric field inside a uniformly charged sphere is

\(\frac{\rho r}{3 \epsilon_{0}}\)

The electric potential inside a uniformly charged sphere

\(=\frac{\rho R^{2}}{6 \epsilon_{0}}\left[3-\frac{r^{2}}{R^{2}}\right]\)

\(\therefore \) Potential difference between centre and surface

\(=\frac{\rho R^{2}}{6 \epsilon_{0}}[3-2]=\frac{\rho R^{2}}{6 \epsilon_{0}}\)

\(\Delta \mathrm{U}=\frac{q \rho R^{2}}{6 \epsilon_{0}}\)