Q.The colour of sky is blue due to (A) interference
(B) scattering
(C) diffraction
(D) polarisation

Scattering of Light

When light passes through a medium containing particles small compared with its wavelength, it is scattered in all directions. According to Rayleigh's law the intensity of scattered light is proportional to $1/\lambda^{4}$, i.e. the scattering power varies as the fourth inverse power of the wavelength.

Because shorter (blue) wavelengths are scattered far more strongly than longer (red) ones, sunlight scattered by air molecules makes the sky appear blue, and the setting Sun looks red because the blue has been scattered away along the long slant path. Rayleigh scattering explains many everyday optical effects in the atmosphere. …