Which of the following phenomena cannot be explained by wave theory of light?

<p><strong>Solution Explanation</strong></p> <p>Among the four listed phenomena:</p> <p><strong>Reflection of light</strong> </p> <p><em>Wave theory</em> (Huygens’s principle, for example) adequately explains reflection.</p> <p><strong>Refraction of light</strong> </p> <p><em>Wave theory</em> also explains refraction via the change of wave speed in different media.</p> <p><strong>Diffraction of light</strong> </p> <p><em>Wave theory</em> (again, Huygens–Fresnel principle) explains the bending of waves around obstacles.</p> <p><strong>Compton effect</strong> </p> <p><p>This involves <em>inelastic scattering of photons</em> by electrons (where the photon loses energy and is scattered with a longer wavelength). </p></p> <p><p><strong>Wave theory alone cannot explain</strong> the discrete energy exchange and wavelength shift; it requires the <em>particle (photon)</em> concept from quantum theory.</p></p> <p>Hence, the phenomenon <strong>not</strong> explained by the (classical) wave theory is the <strong>Compton effect</strong>.</p> <hr /> <p><strong>Answer:</strong> (D) Compton effect.</p>