Final answer:
The rotting of rock by the various types of chemical weathering is most effective in humid regions due to the enhanced ability of moisture to facilitate chemical reactions necessary for weathering.
Step-by-step explanation:
The rotting of rock by the various types of chemical weathering takes place best in humid regions. This is because humidity increases moisture levels in the atmosphere, which facilitates the chemical reactions that lead to the breaking down of rocks. This process is particularly evident in the solution weathering of limestone regions, as evidenced by the solubility equilibria in the formation of karst landscapes, such as those found in the Stone Forest in Yunnan Province, China. High moisture levels catalyze the dissolution of soluble rocks like limestone, and the presence of water in general is a key factor in chemical weathering.
Meanwhile, in arid lands and polar regions, weathering processes occur at a slower rate due to the lack of liquid water. Extreme cold in polar regions inhibits chemical reactions, while arid lands lack the moisture necessary for many chemical weathering processes to occur efficiently. As for upland montane forests, while they may experience significant physical weathering due to freeze-thaw cycles and higher rates of erosion on steep slopes, chemical weathering is less intense compared to humid regions. Therefore, among the options provided, humid regions promote the most rapid chemical weathering of rocks.