Consider the following statements : Statement-I : Rainfall is one of the reasons for weathering of rocks. Statement-II : Rain water contains carbon dioxide in solution. Statement-III : Rain water contains atmospheric oxygen. Which one of the following is correct in respect of the above statements?

Statement-I is correct. Rainfall plays a significant role in various types of weathering, both physical and chemical. For example, direct impact can cause physical weathering, and the presence of dissolved gases in rainwater facilitates chemical weathering.

Statement-II is correct. Rainwater naturally dissolves atmospheric carbon dioxide (CO₂) to form carbonic acid (H₂CO₃), making it slightly acidic. This acidic rainwater is a primary agent of chemical weathering, particularly carbonation, which dissolves carbonate rocks like limestone.

Statement-III is correct. Rainwater also dissolves atmospheric oxygen (O₂). Dissolved oxygen is crucial for the chemical weathering process of oxidation, which is particularly effective in breaking down iron-rich minerals in rocks.

Both Statement-II and Statement-III describe the composition of rainwater (containing dissolved CO₂ and O₂) which contribute to chemical weathering (Statement-I). For instance, carbonic acid from dissolved CO₂ leads to carbonation, and dissolved O₂ leads to oxidation. Both are forms of chemical weathering directly linked to rainfall. Therefore, both Statement-II and Statement-III are correct and collectively explain Statement-I.

Thus, option A is the most appropriate choice.