c
Distance of closest approach when an \(\alpha\) particle of mass \(m\) moving with velocity \(v\) is bombarded on a heavy nucleus of charge \(Z e,\) is given by

\(r_{0}=\frac{Z e^{2}}{\pi \varepsilon_{0} m v^{2}} \) \(\therefore r_{0} \propto \frac{1}{m}\)