Question

mars appears red because its surface is rich in iron oxide. light from mars is highly redshifted as it orbits the sun. the surface of mars is dominated by the centuries - old great red spot. earths atmosphere scatters the shorter wavelength blue light, leaving just the red light to get through to an observer. chemical reactions in its dense atmosphere result in reddish - orange clouds.

Explanation:

Mars has a surface rich in iron - oxide (rust). Iron - oxide gives Mars its characteristic red color. The Great Red Spot is on Jupiter. Red - shift is not the cause of Mars' red color. Earth's atmosphere scattering is not the main reason for Mars' red appearance. Chemical reactions in its atmosphere do not cause its red color.

Answer:

its surface is rich in iron oxide.