A conducting sphere of radius R is given a charge Q. The electric potential and the electric filed at the centre of the sphere respectively are 

Charges reside at the surface of a conductor.

Hence, the electric field$\left(E\right)$ at the centre of the conducting sphere of radius R, is zero.

i.e, $E=0$

and the electric potential $\left(V\right)$  at the centre is given by

$V=\frac{Q}{4{\mathrm{\pi \epsilon }}_0\mathrm{R}}$