When sunlight enters a raindrop and a primary rainbow is formed, which sequence of optical phenomena correctly describes the path of light?

Correct answer: (d) Refraction → Dispersion → Internal reflection → Refraction

Explanation

In a primary rainbow, sunlight undergoes, in order:

• refraction as it enters the raindrop (from air into water);
• dispersion, because water bends violet light more than red light, so the colours separate;
• internal reflection once at the back surface of the drop;
• refraction again as it leaves the drop into the air.

Dispersion happens because of the first refraction, so it cannot come before it. A secondary rainbow involves two internal reflections, which is why its colours are reversed.