Which of the following causes the colour of the clear sky to appear blue at noon?

1. Sunlight contains all visible colours. 2. Air molecules scatter shorter wavelengths much more than longer ones. 3. Blue light, being short, is scattered in all directions across the sky. 4. Observers receive this scattered blue light from every direction overhead. 5. The sky therefore looks blue. 6. So selective scattering of short wavelengths is the cause. _Source: syllabus Science Ch 11 'Human Eye and the Colourful World'_