There is a fixed positive charge Q at O and A and B are points equidistant from O. A positive charge + q is taken slowly by an external agent from A to B along the line AC and then along the line CB.

The work done in moving a charge in an external electric field will be the change in potential energy of the system of particles.

As V_A = V_B; work done in moving a charge from A to B is zero.

As the distance of C from the point O is less than that of point A, so the he work done by the electrostatic force from A to C is negative.

As the distance of C from the point O is less than that of B, So the work done by the electrostatic force from C to B is positive