The radius of the second Bohr orbit for hydrogen atom is : <br> (Planck's constant $h= 6.6262 \times 10^{-34} Js$; mass of electron = $9.1091 \times 10^{-31} kg$; charge of electron $e = 1.60210 \times 10^{-19}C$; permittivity of vacuum $\in_0 = 8.854185 \times 10^{-12} kg^{-1}m^{-3}A^{2}$)
