A point charge of magnitude +1µC is fixed at (0, 0, 0). An isolated uncharged spherical conductor, is fixed with its center at (4, 0, 0) cm. I-he potential and the induced electric field at the centre of the sphere is

Induced charges on surface produce zero potential at centre
$\begin{array}{l}{\mathrm{V}}_{\mathrm{net} }={\mathrm{V}}_{\mathrm{point} \mathrm{ch}\mathrm{arge} }=\frac{1}{4{\mathrm{\pi \epsilon }}_0}\left[\frac{\mathrm{q}}{\mathrm{r}}\right]\\ =9\times {10}^9\times \frac{1\times {10}^{-6}}{4\times {10}^{-2}}=2.25\times {10}^5\mathrm{V}\end{array}$
Net field at the center of sphere is zero, so field produced by induced charge is equal to field produced by point charge but in opposite direction 
Req. field$=-\frac{1}{4{\mathrm{\pi \epsilon }}_0}\left[\frac{\mathrm{q}}{{\mathrm{r}}^2}\right]$
$=-9\times {10}^9\times \frac{1\times {10}^{-6}}{{\left(4\times {10}^{-2}\right)}^2}=-5.625\times {10}^6{\mathrm{NC}}^{-1}$