UPSC CSE Prelims
Question 15
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 ?
View correct answer and explanation
Correct answer: A
Correct Option: A (Both Statement-II and Statement-III are correct and both of them explain Statement-I)
Explanation: Rain causes chemical weathering: dissolved CO₂ forms weak carbonic acid and dissolved O₂ promotes oxidation of minerals. Both mechanisms explain rock alteration.
Statement / Pair / Item-wise Analysis:
I. Correct/True - Rainwater participates in dissolution, carbonation and oxidation.
II. Correct/True - Atmospheric CO₂ dissolves in rainwater to make weak carbonic acid.
III. Correct/True - Dissolved atmospheric oxygen oxidises minerals such as iron compounds.
Option-wise Analysis:
A. Correct-both dissolved CO₂ and O₂ produce chemical processes that weather rock.
B. Incorrect-both gases are present and each explains weathering, not just one.
C. Incorrect-both II and III are true, not only one of them.
D. Incorrect-rainwater contains both dissolved carbon dioxide and dissolved oxygen.