Step 1: Understanding wave vs particle behaviour.
Wave nature is shown when electromagnetic radiation exhibits phenomena such as interference and diffraction. Particle nature is shown in photoelectric effect and Compton scattering.
Step 2: Checking each phenomenon.
(A) Diffraction → bending of waves around obstacles → wave nature → correct.
(B) Interference → superposition of waves → wave nature → correct.
(C) Photoelectric effect → photon knocks out electron → particle nature → incorrect.
(D) Compton scattering → photon-electron collision → particle nature → incorrect.
Step 3: Conclusion.
Thus, diffraction and interference demonstrate the wave nature of electromagnetic radiation.