The electric field intensity at a point lying outside the sphere (non-conducting) is

$E=\frac{1}{4\pi {\epsilon }_0}·\frac{q}{r^2}$

i.e.  $E\propto \frac{1}{r^2} \dots \left(\mathrm{i}\right)$

The electric field intensity at the surface $(r=R)$,

$E=\frac{1}{4\pi {\epsilon }_0}\frac{q}{R^2}$

$\Rightarrow E\propto \frac{1}{R^2}$

where, $R$ being the radius of sphere,

The electric field intensity inside the sphere is

$E=\frac{qr}{4\pi {\epsilon }_0{R}^3}$

$\Rightarrow E\propto r$

At the centre of sphere, $r=0, \therefore E=0$