Fact 1: Chemical weathering causes iron in rock to oxidize. Fact 2: Oxidation of iron minerals causes the redness of the rocks. Given the two facts above, chemical weathering causes redness of the rocks containing what?

Available choices: [I] iron; [II] Urea; [III] Gases; [IV] red stones; [V] matter; [VI] gems; [VII] coal; [VIII] oranges;
The answer is:
[I]