Which of the following characteristics of light conclusively...

According to the corpuscular theory of light, the speed of light in a denser medium should be greater than its speed in a rarer medium. However, experimental determination showed that the speed of light in water is less than its speed in a vacuum. This contradicted the corpuscular theory and provided strong support for the wave theory.

The phenomenon of interference can only be explained by considering the wave nature of light, as particles cannot produce interference patterns (constructive and destructive interference). Thus, it conclusively supports the wave theory.

The photoelectric effect supports the particle (photon) nature of light, not the wave theory.

The laws of reflection can be successfully explained by both the corpuscular and wave theories of light, so they do not conclusively support the wave theory over the particle theory.

Therefore, the lower speed of light in water compared to a vacuum and the phenomenon of interference conclusively support the wave theory of light.