The potential energy between two atoms in a molecule is given by \[U(x)=\frac{a}{{{x}^{12}}}-\frac{b}{{{x}^{6}}}\]; where a and b are positive constants and x is the distance between the atoms. The atom is in stable equilibrium when [CBSE PMT 1995]

• A. \[x=\sqrt[6]{\frac{11a}{5b}}\]
• B. \[x=\sqrt[6]{\frac{a}{2b}}\]
• C. \[x=0\]
• D. \[x=\sqrt[6]{\frac{2a}{b}}\]