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

Question

( A ) $24 \pi a \varepsilon_0 r$
( B ) $-24 \pi a \varepsilon_0 r$
( C ) $-6 a \varepsilon_0 r$
( D ) $-6 a \varepsilon_0$