If the de Broglie wavelength of an electron is equal to the 10–3 times the wavelength of a photon of frequency 6 $ \times 1014 Hz, then the speed of electron is equal to : (Speed of light = 3 \times 108 m/s, Planck's constant = 6.63 \times
10–34 J.s, Mass of electron = 9.1 \times $ 10–31 kg)