As per this diagram a point charge +q is placed at the origin O. Work done in taking another point charge –Q from the point A coordinates (0, a) to another point B coordinates (a, 0) along the straight path AB is

Question

( A ) $[\frac{qQ}{4\pi\epsilon_0}\frac{1}{a^2}]\frac{1}{\sqrt2}$
( B ) $[\frac{-qQ}{4\pi\epsilon_0}\frac{1}{a^2}]\sqrt{2a}$
( C ) Zero
( D ) $[\frac{qQ}{4\pi\epsilon_0}\frac{1}{a^2}]\sqrt{2a}$