A solid coducting sphere having a charge $Q$ is surrounded by an uncharged concentric  conducting hollow spherical shell. Let the potential difference between the surface of the  solid sphere and that of the outer surface of the hollow shell be $V$. If the shell is now  given a charge $-3Q$, the new potential difference between the same two surface is :-........$V$

  • A

    $1$

  • B

    $2$

  • C

    $4$

  • D

    $-2$

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