A charge $+q$ is distributed over a thin ring of radius $r$ with line charge density $\lambda=q \sin ^2 \theta /(\pi r)$. Note that the ring is in the $x-y$ plane and $\theta$ is the angle made by $r$ with the $x$-axis. The work done by the electric force in displacing a point charge $+Q$ from the center of the ring to infinity is

• A

  equal to $\frac{q Q}{8 \pi \epsilon_0 r}$.
• B

  equal to zero only if the path is a straight line perpendicular to the plane of the ring.
• C

  always zero because electrostatic field is conservative.
• Correct answer
  D

  equal to $\frac{q Q}{4 \pi \epsilon_0 r}$.

Hence, the correct answer is option: 'D'.