The de-Broglie wavelength of an electron travelling with 10% of velocity of light is equal to

v = 10% of velocity of light10100×3.0×108m/s=3.0×107m/s m=9.1×10−31 kg λ=hmv=6.6×10−34J−s9.1×10−31×3×107 24.2×10−12m=24.2 pm