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 ?
Show answer
Answer: A. Statement I is correct: rain is a major cause of chemical weathering. Statement II is correct: rain dissolves carbon dioxide, forming weak carbonic acid that dissolves rocks such as limestone (carbonation). Statement III is correct: rain water carries dissolved oxygen, which oxidises iron-bearing minerals (oxidation). Both II and III explain I.
Watch for: Students often link rain only to carbonic acid and forget that dissolved oxygen also drives weathering through oxidation.
Why the other options are wrong
- B. Wrong because both carbonation and oxidation explain chemical weathering by rain.
- C. Wrong because both Statements II and III are correct.
- D. Wrong because rain water does contain both dissolved carbon dioxide and oxygen.
Source to check: NCERT Class 11 Fundamentals of Physical Geography, Chapter 5 'Geomorphic Processes' (chemical weathering: carbonation, oxidation)
Answer from the official UPSC key. Written and fact-checked by AI against the official key. Spotted a mistake? Report it.