Trace the path of a single ray of sunlight through one raindrop step by step.
- The ray hits the curved front surface of the droplet and bends as it enters, because light slows down going from air into water. This bending, refraction, is different for each colour, so the white light begins to spread into its component colours.
- The ray travels to the back inner surface of the droplet, where it reflects instead of escaping, because the angle of incidence there is large enough for total internal reflection to occur.
- The reflected ray now travels back toward the front of the droplet and refracts a second time as it leaves the drop into the air, bending and spreading the colours even further apart.
Millions of droplets across the sky each send one colour toward your eye at a very specific angle, and together they paint the familiar arc of colours we call a rainbow. The two processes at work here, refraction with dispersion, and internal reflection, are exactly what option A describes, so A is correct.