Step 1: Electric Field Inside a Charged Sphere.
For a uniformly charged sphere, the electric field inside the sphere at a distance \( r \) from the center is given by:
\[
E = \frac{r^2 \rho}{3 \epsilon_0}
\]
where \( \rho \) is the charge density and \( \epsilon_0 \) is the permittivity of free space.
Step 2: Conclusion.
The correct answer is (D), \( \frac{r^2 \rho}{3 \epsilon_0} \).