Dual Nature of Matter and Radiation — quick quiz

In the Davisson-Germer experiment, electrons accelerated through 54 V showed a strong diffraction peak at an angle of 50° to the incident beam. If the spacing between atomic layers in the nickel crystal was 0.091 nm, what is the order of diffraction observed? (Given: h = 6.63 × 10⁻³⁴ J·s, mass of electron = 9.1 × 10⁻³¹ kg, e = 1.6 × 10⁻¹⁹ C, sin 25° = 0.42)