Four equal charges Q are placed at the four corners of a square of side a  each. Work done in removing a charge -Q from its centre to infinity is

The potential at the center of the square of side a due to four equal charges Q at the corners=4×14πε0×Q(a/2)=2⋅Qπε0aWork done = potential difference x charge               =2Qπε0a×Q=2Q2πε0a