Explanation:

- Weathering (Option 2): This is the correct answer. Weathering is the process that involves the breaking down of rocks on the Earth’s surface due to various factors like temperature changes, water, and biological activity.

- Conurbation (Option 1): This term refers to the merging of several urban areas or cities into a large, continuous urban area, and is unrelated to rock formations.

- Desertification (Option 3): This term describes the process by which fertile land becomes desert, usually as a result of drought, deforestation, or inappropriate agriculture. It does not involve breaking down rocks.

- Flacking (Option 4): This option is likely intended to be "flaking," which refers to a surface breaking into thin layers or pieces, but it is not a standard term for rock breaking.