A block of mass $m$ containing a net negative charge $-q$ is placed on a frictionless  horizontal table and is connected to a wall through an unstretched spring of spring  constant $k$ as shown. If horizontal electric field $E$ parallel to the spring is switched on,  then the maximum compression of the spring is :-
  • A$ \sqrt {qE / k}$
  • B$ \sqrt {k / qE}$
  • C$qE/k$
  • D$\frac{2qE}{k}$
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