In the relation between the field and the potential, if r < a, then the potential at a point r inside a uniformly charged sphere of radius a, is

A. $$\frac{{{a^3}\rho }}{{3{\varepsilon _0}r}}$$

B. $$\frac{\rho }{{6{\varepsilon _0}}}\left( {3{a^2} - {r^2}} \right)$$

C. $$\frac{{4\pi {a^3}}}{{3r}}$$

D. $$\frac{{2\pi }}{3}\left( {3{a^2} - {r^2}} \right)$$

Answer: Option B