In chemical weathering, oxygen plays a major role in which process?

Correct answer: Oxidation

Direct answer: Option D, oxidation. Chemical weathering changes the minerals within a rock. During oxidation, oxygen reacts with minerals, especially iron-bearing minerals, producing oxides. The result may look reddish or brown, much like rust on iron. Water often helps the reaction, but the key chemical agent named in this question is oxygen. Option A is wrong because exfoliation is mainly a physical process in which outer layers peel away, often due to pressure release or temperature effects. Option B is wrong because frost action is physical weathering caused by freezing and expansion of water in cracks. Option C is wrong because salt crystallization is physical weathering in which growing salt crystals exert pressure. Option D is correct because it directly names the oxygen-mineral reaction. Memory cue: oxygen plus iron gives rust-like oxidation.