The correct option is that both Statement-II and Statement-III are correct and explain Statement-I. Rainfall contributes to the weathering of rocks by facilitating chemical reactions; the carbon dioxide dissolved in rainwater (Statement-II) forms carbonic acid, which enhances the chemical weathering of minerals in rocks, particularly limestone. Additionally, the presence of atmospheric oxygen (Statement-III) can lead to oxidation reactions, further breaking down rocks and minerals. Together, these processes highlight how rainfall not only leads to physical weathering but also significantly enhances chemical weathering through its chemical composition.