The ratio of de-Broglie wavelength of a $\;\alpha\;$ particle to that of proton being subjected to same magnetic field so that the radii of their path are equal to each other assuming the field induction vector $\;\overrightarrow{B}\;$ is perpendicular to velocity vectors of $\;\alpha-\;$ particle and proton , is

Question

$(a)\;1\qquad(b)\;\large\frac{1}{4}\qquad(c)\;\large\frac{1}{2}\qquad(d)\;2$