The correct answer is (d).
The brilliance of diamond is due to total internal reflection of light. When light enters a diamond from air, it is refracted (bent) and then reflected off the back of the diamond. The light is then refracted again as it exits the diamond. This process of refraction and reflection causes the light to be scattered in all directions, which gives diamonds their brilliant appearance.
(a) Interference of light is the phenomenon that occurs when two or more waves of light meet and interfere with each other. This can cause the waves to cancel each other out, or to reinforce each other, depending on the difference in their wavelengths. Interference is not the main cause of the brilliance of diamond.
(b) Diffraction of light is the bending of light as it passes through a narrow opening or around an obstacle. This is caused by the wave nature of light. Diffraction is not the main cause of the brilliance of diamond.
(c) Polarization of light is the process of restricting the direction of oscillation of light waves. This can be done by passing light through a polarizing filter. Polarization is not the main cause of the brilliance of diamond.