The angles of incidence with respect to the normal will the x-rays reflect from the crystal will be
16.60 degrees. Given: wavelength of X-rays, λ= 0.120 nm
Distance, d=0.21 nm
According to Bragg’s diffraction law: nλ = 2dsinθ
thus, 0.120 = 2*0.21sinθ
or θ =
(0.120/2*0.21)
or θ = 16.60 degrees.