Rainbow formation is a natural phenomenon illustrating that white light

Analyze the question: A rainbow is formed when sunlight (white light) passes through raindrops. The question asks what this natural phenomenon illustrates about white light.

Concept: Dispersion of light White light is made up of seven constituent colours: red, orange, yellow, green, blue, indigo and violet (ROYGBIV). When white light passes from one medium to another (air to water), each colour bends (refracts) by a different amount because each has a different wavelength and speed in the medium. Violet bends the most and red the least. This separation into colours is called dispersion.

How a rainbow forms (step by step):

1. Sunlight enters a raindrop and is refracted, and dispersion begins.
2. The light is internally reflected at the back of the drop.
3. It is refracted again as it leaves the drop, and the colours spread out further.
4. The observer sees the separated colours as a band of colour in the sky.

Checking the options:

• A. Wrong. White light splits into seven colours, not three, and it is not simply "after rainfall" as a statement of the principle.
• B. Dispersion by glass prisms is true, but the question asks what a rainbow illustrates, which involves raindrops, not prisms.
• C. Wrong. The splitting happens as light passes through the raindrops, not before rainfall.
• D. Correct. The rainbow appears after rainfall, when water droplets are still in the air, and white light is dispersed into its constituent colours.

Tip: Link keywords to concepts. "Rainbow" means dispersion by raindrops, so look for "dispersed into constituent colours". Also remember that a rainbow is seen when the Sun is behind you and rain is in front of you.