• Statement I: This statement is true. Rainfall is one of the reasons for the weathering of rocks.  Rainwater can cause both physical and chemical weathering. Physical weathering occurs due to the impact of raindrops, especially during heavy downpours. Chemical weathering happens when rainwater reacts with minerals in rocks, leading to their breakdown.

• Statement-II: This statement is true. Rainwater contains carbon dioxide in solution. Rainwater absorbs carbon dioxide from the atmosphere, forming weak carbonic acid (H2CO3). This slightly acidic nature of rainwater contributes to chemical weathering.

• Statement-III: This statement is true. Rainwater contains atmospheric oxygen. Rainwater dissolves atmospheric gases, including oxygen. The dissolved oxygen in rainwater plays a role in the oxidation of certain minerals in rocks, which is a form of chemical weathering.

Therefore, both Statement II and Statement III are correct, and both explain Statement I. Rainwater's acidity (due to dissolved carbon dioxide) and dissolved oxygen content contribute to the chemical weathering of rocks.