The diagram indicates two points P and Q that are separated by $90^{\circ}$, on a circle of radius $r$. A positive point charge placed at the centre of the circle produces an electric field of magnitude $E$ at both P and Q. Which expression gives the work done in moving a unit positive charge from P to Q?
- A$0$
- B$E \times r$
- C$E \times \left(\frac{\pi r}{2}\right)$
- D$E \times (\pi r)$