Let $P ( r ) = \frac { Q } { \pi R ^ { 4 } } r$ 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\\
(1) 0\\
(2) $\frac { Q } { 4 \pi \varepsilon _ { 0 } r _ { 1 } ^ { 2 } }$\\
(3) $\frac { Q r _ { 1 } ^ { 2 } } { 4 \pi \varepsilon _ { 0 } R ^ { 4 } }$\\
(4) $\frac { Q r _ { 1 } ^ { 2 } } { 3 \pi \varepsilon _ { 0 } R ^ { 4 } }$