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?

Question

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?

Accepted Answer

Both Statement-II and Statement-III are correct and both of them explain Statement-I Quick Verdict: As rain falls, it naturally dissolves atmospheric gases. By holding both carbon dioxide and oxygen in solution, rainwater actively triggers chemical weathering processes—specifically carbonation and oxidation—which break down rocks. Therefore, both Statement-II and Statement-III correctly explain Statement-I. Thematic Discussion: Chemical Weathering by Rainfall As rain falls through the atmosphere, it acts as a natural solvent, absorbing various atmospheric gases. This transforms ordinary precipitation into a highly active agent of chemical weathering. Carbonation (Statement-II): Rainwater dissolves atmospheric carbon dioxide to form a weak acid known as carbonic acid. This slightly acidic water reacts aggressively with carbonate-rich rocks, such as limestone and chalk, gradually dissolving them completely over time. Oxidation (Statement-III): Rainwater also dissolves atmospheric oxygen. When this oxygen-enriched water comes into contact with minerals in the rocks—especially iron-bearing rocks like pyrite—it causes them to oxidize (a process essentially identical to "rusting"). This chemical alteration severely weakens the structural integrity of the rock, causing it to crumble. Because both dissolved carbon dioxide and dissolved oxygen actively drive these distinct degradation processes, both are directly responsible for the weathering of rocks. (Reference: Class 11 NCERT, Fundamentals of Physical Geography, Chapter 6, Chemical Weathering Processes) (Reference: G.C. Leong's Certificate Physical and Human Geography, Chapter 4 and 5, Chemical Weathering)