$A$ and $B$ are two identical blocks made of a conducting material. These are placed on a horizontal frictionless table and connected by a light conducting spring of force constant $K$. The unstretched length of the spring is $L_0$. $A$ charge $Q/2$ is given to each block. Consequently,the spring stretches to an equilibrium length $L$. The value of $Q$ is

• A
  $\sqrt {4\pi {\varepsilon _0}KL} $
• B
  $L\sqrt {\frac{K}{{4\pi {\varepsilon _0}\left( {L - {L_0}} \right)}}} $
• C
  $2L\sqrt {4\pi {\varepsilon _0}K\left( {L - {L_0}} \right)} $
• D
  $4\pi {\varepsilon _0}K\left( {L - {L_0}} \right)$