Assertion :Blue colour of sky appears due to scattering of light. Reason: Blue colour has shortest wavelength among all colours of white light.

The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion

1. Scattering of sunlight through molecules of atmosphere is the reason for the blue of the sky.
   
2. Our atmosphere contains atoms and molecules of different sizes.
   
3. According to their sizes they are able to scatter different wavelength of light.
   
4. For example, the size of the water molecule is greater than the size of the $N_2$ or $O_2$
   
5. It acts as scattering centre for other frequencies which are lower than the frequency of blue light.
   
6. Blue colour scatters more than other colours.
   
7. That is why sky appears blue.