A point charge + q is placed at the origin as shown in fig. Work done in taking another point charge -Q from point A (0,a) to another point B (a,0) along the straight paths AB is

• A

  zero

• B

  $\left(\frac{\mathrm{qQ}}{4{\mathrm{\pi \epsilon }}_0}\times \frac{1}{{\mathrm{a}}^2}\right)\sqrt{2}\mathrm{a}$

• C

  $\left(\frac{-\mathrm{qQ}}{4{\mathrm{\pi \epsilon }}_0}\times \frac{1}{{\mathrm{a}}^2}\right)\sqrt{2}\mathrm{a}$

• D

  $\left(\frac{\mathrm{qQ}}{4{\mathrm{\pi \epsilon }}_0}\times \frac{1}{{\mathrm{a}}^2}\right)\frac{\mathrm{a}}{\sqrt{2}}$