If potential energy function for the force between two atoms in a diatomic molecule is approximately given by $U\left(x\right)=\frac{\mathrm{a}}{x^8}-\frac{\mathrm{b}}{x^4}$, where $\mathrm{a}$ and $\mathrm{b}$ are constants in standard SI units and $x$ is in metres. Find the dissociation energy of the molecule (in $\mathrm{J}$). [Take $\mathrm{a}=4 \mathrm{J} {\mathrm{m}}^8$ and $\mathrm{b}=20 \mathrm{J} {\mathrm{m}}^4$]

Hence, the correct answer is 25.