A neutron, a proton, an electron and an alpha particle enter a region of constant magnetic field with equal velocities. The magnetic field is along the inward normal to the plane of the paper. The tracks of the particles are lebelled in Fig. The electron follow track......... and the alpha particle follow track..........

Explanation

According to Fleming's left hand rule, the force on electrons
will be toward right (D).
Also, by the same rule we find that the force on proton and
`alpha`- particle is twoward left.
Now, since the magnetic force will behave as centripetal force
`:. (mv^2)/r=qvB implies (mv)/(qB) =r or rpropm/q`
For proton `rprop1/1=1,` For `alpha`-particle `rprop4/2=2`
`:.` Radius will be greater for `alpha`-particle
`:. alpha`-particle will take path B.