The potential energy of a diatomic molecule is given by $U = \frac{A}{{{r^{12}}}} - \frac{B}{{{r^6}}}$ . $A$ and $B$ are positive constants. The distance $r$ between them at equilibrium is 

  • A

    ${\left( {\frac{A}{B}} \right)^{1/6}}$

  • B

    ${\left( {\frac{{2A}}{B}} \right)^{1/6}}$

  • C

    ${\left( {\frac{A}{{2B}}} \right)^{1/6}}$

  • D

    None of these

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