Let $\rho(r)=\left(\frac{Q}{\pi R^{4}} r\right)$ be the charge density distribution for a solid sphere of radius $R$ and total charge $Q .$ For a point $P$ inside the sphere at distance $r_{1}$ from the centre of the sphere, the magnitude of electric field is
(a) zero
(b) $\frac{Q}{4 \pi \varepsilon_{o} r_{1}^{2}}$
(c) $\frac{Q r_{1}^{2}}{4 \pi \varepsilon_{o} R^{4}}$
(d) $\frac{Q r_{1}^{2}}{3 \pi \varepsilon_{o} R^{4}}$