Concept:A rainbow forms when water droplets separate white sunlight into its component colours.Explanation:When sunlight enters a water droplet, the light bends as it passes from air into water.Different colours of light bend by different amounts because each colour travels at a slightly different speed in water.This separation of white light into a band of colours is called dispersion.The light also reflects inside the droplet and bends again when leaving it, which makes the full rainbow visible.Answer:C. dispersion