Which of the following phenomena contributes most to the sun's reddish hue at sunrise and sunset?

•  Scattering of light is when a light ray is redirected in all other directions after passing through particles with dimensions comparable to the wavelength of the light used.
• White light has seven colours: violet, indigo, blue, green, yellow, orange, and red. The wavelength of red light is the longest of the seven constituent colours.
• More colours are scattered during the sunset and sunrise hours because light must travel a greater distance. 
• However, red light does not scatter much due to its long wavelength and reaches our eyes.
• Therefore, the sky appears red.

Hence, 'Light Scattering' is the correct response.