Chemical weathering and mechanical weathering are two processes that contribute to the breakdown and alteration of rocks on the Earth's surface. Chemical weathering involves the chemical alteration of minerals in rocks through processes such as dissolution, oxidation, and hydrolysis. Mechanical weathering, on the other hand, involves the physical breakdown of rocks into smaller fragments through processes such as freeze-thaw cycles, abrasion, and root wedging.

Among the given options, the region where chemical weathering process is more dominant than the mechanical process is the limestone region (option C). This is because limestone is composed mainly of calcium carbonate, which is highly susceptible to chemical weathering.

Now let's understand why chemical weathering is more dominant in limestone regions:

1. Composition of Limestone:
- Limestone is primarily composed of calcium carbonate (CaCO3), which is a mineral highly susceptible to chemical weathering.
- The presence of calcium carbonate makes limestone highly reactive with acids, water, and other chemical agents.

2. Carbonation:
- Carbonation is a chemical weathering process that occurs in limestone regions.
- Rainwater combines with carbon dioxide (CO2) in the atmosphere to form a weak carbonic acid (H2CO3).
- This carbonic acid reacts with the calcium carbonate in limestone, gradually dissolving it and forming calcium bicarbonate (Ca(HCO3)2), which is soluble in water.
- Over time, this process leads to the dissolution and erosion of limestone formations, resulting in the formation of caves, sinkholes, and underground drainage systems.

3. Karst Topography:
- Karst topography is a distinctive landscape formed by the dissolution of soluble rocks, such as limestone.
- Chemical weathering processes, particularly carbonation, play a significant role in the development of karst topography.
- As limestone dissolves, it creates intricate networks of underground caves, sinkholes, and underground rivers.

4. Minimal Mechanical Weathering:
- Limestone is a relatively soft rock compared to other types of rocks.
- Mechanical weathering processes, such as freeze-thaw cycles or abrasion, have a limited impact on limestone due to its composition.
- In limestone regions, chemical weathering is therefore more dominant compared to mechanical weathering.

In conclusion, the chemical weathering process is more dominant than the mechanical process in limestone regions due to the composition of limestone, the occurrence of carbonation, the formation of karst topography, and the relatively minimal impact of mechanical weathering on limestone.