Explanation

(a) In 1927 at Bell Labs, Clinton Davisson and Lester Germer fined slow moving electrons at a crystalline nickel target. The angular dependence of the reflected electron intensity was measured and was determined to have the same difffraction
pattern as those predicted by Bragg for X-rays. This experiment, proved the wave like nature of matter and completed the wave particle duality hypothesis, which was a fundamental step in quantum theory.
While Compton scattaering or Compton effect observed by Arthur Holly Compton in 1927, proved the particle nature of light.