A $20 \mathrm{cm}$ long metallic rod is rotated with $210 \mathrm{rpm}$ about an axis normal to the rod passing through its one end. The other end of the rod is in contact with a circular metallic ring. A constant and uniform magnetic field $0.2 \mathrm{T}$ parallel to the axis exists everywhere. The emf developed between the centre and the ring is _________$\mathrm{mV}$.

(Take $\pi =\frac{22}{7}$)

Hence, the correct answer is 88.