The electrostatic potential inside a charged spherical ball is given by $$\phi = \alpha r^2 + b$$ where $$r$$ is the distance from the centre; $$a, b$$ are constants. Then the charge density inside ball is:

A

$$-6 a \varepsilon_0 r$$

B

$$-24 \pi a \varepsilon_0$$

C

$$-6 a \varepsilon_0$$

D

$$-24 \pi a \varepsilon_0 r$$