To slow down the process of chemical weathering, the most effective action among the options provided is burning less fossil fuel. This action indirectly helps to reduce the amount of atmospheric carbon dioxide and other pollutants that contribute to acid rain, which can accelerate chemical weathering processes.
The other options either do not have a significant impact on chemical weathering (like removing clay, which is not a primary driver of weathering) or do not address the chemical processes directly related to the weathering of rocks.