Two unlike charges of magnitude q each are separated by a distance 2d. The potential at a point midway between them is 

• A

  Zero

• B

  $\frac{1}{4{\mathrm{\pi \epsilon }}_0}$

• C

  $\frac{1}{4{\mathrm{\pi \epsilon }}_0}.\frac{\mathrm{q}}{\mathrm{d}}$

• D

  $\frac{1}{4{\mathrm{\pi \epsilon }}_0}.\frac{2\mathrm{q}}{{\mathrm{d}}^2}$