As sunlight reaches our atmosphere, molecules in the air scatter the blue light but let the red light pass through.
A molecule is the smallest unit of a substance that has all the properties of that substance. For instance, a. water molecule is the smallest unit that is still water.
An atom has a nucleus surrounded by electrons. Another difference between atoms and molecules is that when similar atoms combine in varying numbers, molecules of different properties can be formed.
Colour and wavelength 
There are seven wavelength ranges within the visible spectrum more that each correspond to a different colour. The colours fall in an order commonly referred to with the memory aid ROYGBIV. [Roy, Great Britain, (Four) IV) ]
ROYGBIV can aid in remembering the order of the colours: red, orange, yellow, green, blue, indigo, and violet.
Red has the longest wavelength and violet has the shortest wavelength. When all the waves are seen together, they make white light.
