You are presented with the question "chemical weathering causes redness of the rocks containing what?" and the following answer choices: 
- iron
 - Urea
 - Gases
 - red stones
 - matter
 - gems
 - coal
 - oranges

Now knowing that chemical weathering causes iron in rock to oxidize and oxidation of iron minerals causes the redness of the rocks, choose the best answer.


 

 iron        