The spread in colors in a rainbow in the sky is primarily due to option 1, dispersion of sunlight.
Dispersion is the phenomenon where light is separated into its different wavelengths or colors. When sunlight passes through raindrops in the atmosphere, it gets dispersed or spread out. This happens because different colors of light have different wavelengths and when they enter a different medium, such as a raindrop, they bend or refract at different angles. This bending or refraction causes the different colors to spread out and form a spectrum.
In the case of a rainbow, this dispersion of sunlight inside the raindrop leads to the formation of a circular arc of colors in the sky. The colors that we see in a rainbow, such as red, orange, yellow, green, blue, indigo, and violet, are all a result of this dispersion of sunlight.
Option 2, reflection of sunlight, is not correct because reflection does not cause the separation of colors that we see in a rainbow.
Option 3, refraction of sunlight, is the correct explanation as refraction is the bending of light when it passes from one medium to another, causing the spread of colors.
Option 4, total internal reflection of sunlight, is not correct as total internal reflection