Question

sun looks red at the time of setting

Answer 1

during sunrise and sunset the rays have to travel a larger part of atmosphere because they are very close to horizon

Answer 2

Hey !!

At the time of setting, the sun is at horizon. The light emitted by the sun has to travel a relatively longer distance through the atmosphere. As a result blue part of light is scattered away by the particles in the atmosphere causing red part to be visible.

Good luck !!