Question

why sky is red in sunset

Answer 1

Within the visible range of light, redlight waves are scattered the least by atmospheric gas molecules. So at sunrise and sunset, when the sunlight travels a long path through the atmosphere to reach our eyes, the blue light has been mostly removed, leaving mostly red and yellow light remaining.

Answer 2

during sunset as the sun is very far from US and The White lights get splits into seven colours as the red colour has more scattering that's why we can see the red colour during sunset