Four charges each equal to q are placed at the corners  of a square of side I The electric potential at the centre of the square is 

• A

  $\frac{1}{4{\mathrm{\pi \epsilon }}_0}\times \frac{4\mathrm{q}}{\mathrm{l}}$

• B

  $\frac{1}{4{\mathrm{\pi \epsilon }}_0}\times \frac{4\mathrm{q}}{\sqrt{2}\cdot \mathrm{l}}$

• C

  $\frac{1}{{\mathrm{\pi \epsilon }}_0}\times \frac{\sqrt{2}\cdot \mathrm{q}}{\mathrm{l}}$

• D

  $\frac{1}{{\mathrm{\pi \epsilon }}_0}\times \frac{2\mathrm{q}}{\mathrm{l}}$