The following experiment suggests that light propagates as waves

The correct answer is Option (3) → Young's Double slit experiment

Only interference and diffraction can be explained by waves and not by particles. The experiment that shows light behaving as a wave is the one that produces an interference pattern.

Option (3) Young's Double slit experiment — Correct. Light from two slits overlaps and forms bright and dark interference fringes, which only waves can produce.

NCERT (2026-27):
Wave Nature of Matter – “The dual (wave-particle) nature of light (electromagnetic radiation, in general) comes out clearly from what we have learnt in this and the preceding chapters. The wave nature of light shows up in the phenomena of interference, diffraction and polarisation. On the other hand, in the photoelectric effect and Compton effect which involve energy and momentum transfer, radiation behaves as if it is made up of a bunch of particles — the photons.”