A uniform flexible chain of mass $m$ and length $2l$ hangs in equilibrium over a smooth horizontal pin of negligible diameter. One end of the chain is given a small vertical displacement so that the chain slips over the pin. The speed of chain when it leaves pin is

  • A

    $\sqrt {2gl}$

  • B

    $\sqrt {gl}$

  • C

    $\sqrt {4gl}$

  • D

    $\sqrt {3gl}$

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