Total Internal reflection The total reflection of light from a higher refractive index medium to back in its medium at an angle more than a critical angle known as total internal reflection.
Refraction When a ray of light passes from one medium to another it suffers a change in direction at the boundary of two media is called refraction.
The change in direction because the speed of light travels at different speeds ;in different mediums.
The Refractive Index of a medium defines that it is denser or rarer
Diffraction In diffraction, when a light wave encounters an obstacle or a slit, it bends around the corners of the obstacle or aperture Hence, it is a wave phenomenon.
Dispersion of light: The splitting of white light , when it passes through a glass prism into its constituent spectrum is known as the dispersion of light.
Sunlight splits into 7 colors – Violet, Indigo, Blue, Green, Yellow, Orange, and Red (VIBGYOR).
A rainbow is a natural phenomenon showing dispersion.
EXPLANATION :
From the above discussion, we can say that
Splitting of light into its constituent colours is known as Dispersion of light . So option 4 is correct.