Q: Why sky looks blue ?
Sol: Blue colour of sky is due to scattering of sunlight. Light from the sun, while traveling through earth’s atmosphere gets scattered by large number of molecules in the earth’s atmosphere. The molecules of air and other fine particles in the atmosphere have size smaller than the wavelength of visible light. These are more effective in scattering light of shorter wavelength. As the blue colour has shorter wavelength than red, therefore, blue colour is scattered much more strongly. Hence the sky looks blue.