Wavelength of an electron is $5\text{A}°$.Velocity of the electron is

The De-Broglie wave equation is

$\lambda =\frac{h}{mv}$                                  

$\lambda =5\text{Å}=5\times {10}^{-8}\text{cm}$

And $\text{Planck's\hspace{0.17em}constant\hspace{0.17em}\hspace{0.17em}}h=6.625\times {10}^{-27}\text{ergs/sec}$

Then velocity of electron is

$v_e=\frac{h}{\lambda m}$                                 

Mass of electron is

$m_e=9.1\times {10}^{-28}\text{g}$

$\text{v}=\frac{6.625\times {10}^{-27}}{5\times {10}^{-8}\times 9.1\times {10}^{-28}}$

$\therefore v_e=1.45\times {10}^8\text{cm/sec}$