The correct answer is D. Polarisation.
Polarization is the property of waves that have an orientation, such as electromagnetic waves and sound waves. The orientation of the wave is perpendicular to the direction of the wave’s motion.
Polarization was first observed in light in 1808 by the French physicist François Arago. He found that when light passed through a polarizing filter, it was only able to pass through if the filter was aligned with the orientation of the light waves. This showed that light waves have an orientation, and therefore must be transverse waves.
Transverse waves are waves in which the particles of the medium move perpendicular to the direction of the wave’s motion. Examples of transverse waves include water waves, sound waves in a string, and light waves.
Reflection, interference, and diffraction are all phenomena that can occur with both transverse and longitudinal waves. However, polarization can only occur with transverse waves. This is because the orientation of the wave is perpendicular to the direction of the wave’s motion, and therefore cannot be affected by the medium through which the wave is traveling.
In conclusion, the phenomenon which established the transverse nature of light is polarization.