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Rainbow is formed with seven colours I.e is "VIBGYOR". It appears due to the water droplets break sunlight into seven colours of spectrum. The water droplets in the atmosphere acts as a prism through which the traces of light are very complex
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The Brainliest Answer!
After the rain a number of small droplets of water remain suspended in the air. Each drop acts as a small prism. When sunlight falls on these drops the white light spills into seven colours. The dispersed light from a large number of drops forms a continuous band of seven colours. 
This coloured band is called a RAINBOW.
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