The value of de-Broglie wavelength of an electron moving with a speed of $6.6\times {10}^5{ \mathrm{ms}}^{-1}$ is approximately 

[$\mathrm{h}=6.6\times {10}^{-34} \mathrm{Js}$ , $\text{ mass of electron }=9\times {10}^{-31} \mathrm{kg}$]