Which process involves the combination of rainfall with carbon dioxide to form a weak acid?

The process that involves the combination of rainfall with carbon dioxide to form a weak acid is carbonation-solution. When rainwater absorbs carbon dioxide from the atmosphere, it reacts to form carbonic acid (H2CO3). This weak acid is significant in the weathering of minerals, especially limestone and other carbonate rocks, as it enhances the dissolution of these materials, facilitating the process of chemical weathering. The formed carbonic acid interacts with minerals, leading to their breakdown and the release of essential nutrients into the soil, which can then be utilized by plants.

In this context, other processes mentioned do not specifically involve the formation of a weak acid from the combination of rainfall and carbon dioxide. Hydration refers to the incorporation of water into a substance, oxidation involves the reaction with oxygen which leads to the alteration of minerals, while chemical weathering is a broader term that encompasses various processes including carbonation but is not specifically defined by the reaction with carbon dioxide. Thus, carbonation-solution is the most accurate choice for this particular process.