Question

Which of the following particles will have minimum frequency of revolution when projected with the same velocity perpendicular to a magnetic field?
(a) Electron
(b) Proton
(c) He⁺
(d) Li⁺

Answer 1

(d) Li⁺

Time period of the revolution of the particle, $T=\frac{2\mathrm{\pi }m}{qB}$
As frequency is the reciprocal of time period, so $f=\frac{qB}{2\mathrm{\pi }m}$
The charge on all the four particles is same. But the mass is maximum for Li⁺. So, it will have the smallest frequency of revolution.