In a uniform magnetic field, the magnetic needle has a magnetic moment $9.85\times {10}^{-2} \mathrm{A} {\mathrm{m}}^{-2}$ and moment of inertia $5\times {10}^{-6} \mathrm{kg}{ \mathrm{m}}^2.$ If it performs $10$ complete oscillations in $5$ seconds then the magnitude of the magnetic field is ____$\mathrm{mT}$  [Take ${\pi }^2$ as $\left.9.85\right]$

Hence, the correct answer is 8.