An electron of mass m_e orbits an alpha particle of mass m_α in a circular orbit of radius r. Which expression gives the speed of the electron?

A.     \(\sqrt {\frac{{2k{e^2}}}{{{m_e}r}}} \)

B.     \(\sqrt {\frac{{2k{e^2}}}{{{m_a}r}}} \)

C.     \(\sqrt {\frac{{4k{e^2}}}{{{m_e}r}}} \)

D.     \(\sqrt {\frac{{4k{e^2}}}{{{m_a}r}}} \)

A