A block having mass m and charge q is resting on a frictionless plane at a distance L from the wall as shown. A uniform electric field E is switched on as shown. If the collision of the block with wall is perfectly elastic, the time taken by the block to return to the initial position is
 

 

• A

  $\sqrt{\frac{\text{2mL}}{\text{Eq}}}$

• B

  $2\pi \sqrt{\frac{\text{mL}}{\text{Eq}}}$

• C

  $2\sqrt{\frac{\text{2mL}}{\text{Eq}}}$

• D

  $\sqrt{\frac{\text{mL}}{\text{Eq}}}$