At sunrise and sunset the sun appears reddish due to

scattering of light

The correct answer is Option (1) → scattering of light

At sunrise and sunset, sunlight passes through a longer path in the atmosphere. Shorter wavelengths (blue and violet) are scattered more, leaving the longer wavelengths (red and orange) to reach the observer.

This is due to scattering of light (Rayleigh scattering).

Final Answer: scattering of light