the answer is actually A. chemical weathering by oxidation .
chemical weathering works on rocks that contain iron. These rocks turn to rust in a process called oxidation. Rust is a compound created by the interaction of oxygen and iron in the presence of water.
Answer: A. chemical weathering by oxidation
Weathering is a natural process in which the rock is broken down into small pieces and sediments under the influence of agents like wind, water and chemicals. Chemical weathering is a process in which the rocks breaks down due to the effect of the chemicals. It brings change in the chemical composition of the broken pieces and sediments distinct from the parent rock.
Rust on rocks is a an example of chemical weathering by oxidation. The rock mainly exhibiting elements which can be easily oxidized such as iron undergoes rusting this occurs because oxygen breaks the bonds between the elements in the rock. The internal structure of the rock becomes weak and results in rusting.