Which factor is responsible for the red color of Mars?

sulphur dioxide

methane

iron oxide

nitrogen

The best answer is iron oxide.

Also known as the red planet, the red color of Mars is die to that its regolith (surface material) contains high amount of iron oxide, which is the same compound that renders blood and rust red.

The iron oxide in Mars is thought to have formed long ago. The rusty material was spread around the planet in the huge dust storms that are so characteristic of the this planet.

The red color caused the Greeks of ancient times to give it the name of their god of war.