Potential energy as a function of $r$ is given by $U = \frac{A}{r^{10}} - \frac{B}{r^{5}}$,where $r$ is the interatomic distance,and $A$ and $B$ are positive constants. The equilibrium distance between the two atoms will be

• A
  $\left(\frac{A}{B}\right)^{\frac{1}{5}}$
• B
  $\left(\frac{B}{A}\right)^{\frac{1}{5}}$
• C
  $\left(\frac{2A}{B}\right)^{\frac{1}{5}}$
• D
  $\left(\frac{B}{2A}\right)^{\frac{1}{5}}$