Light from the sun travels through space to earth's atmosphere.

which will light waves do when they move from empty space into matter made up of different gases?

a. move at the same speed
b. move faster as they transmit
c. slow down and refract
d. speed up and reflect

I think the correct answer from the choices listed above is option C. The light waves slow down and refract when they move from empty space into matter made up of different gases. Light does not travel as fast through a non vacuum, and any change in velocity results in a refraction.