A neutron of $K$. E. 50 ev is describing a circular orbit of radius $0.5 \mathrm{~m}$ in a plane perpendicular to magnetic field $\mathrm{B}^{-}$. The $\mathrm{K} . \mathrm{E}$. of the proton that describe a circular orbit of radius
$0.5 \mathrm{~m}$ in the same plane with the same $\mathrm{B}^{-}$ is
(a) $200 \mathrm{ev}$
(b) $100 \mathrm{ev}$
(c) $50 \mathrm{ev}$
(d) $25 \mathrm{ev}$