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?
Answer & explanation
Answer: (a) Both Statement-II and Statement-III are correct and both of them explain Statement-I
Chemical weathering works through water, oxygen and carbon dioxide. Falling rain dissolves both gases from the air: the dissolved carbon dioxide forms a weak acid that attacks rocks (carbonation), and the dissolved oxygen oxidises minerals such as iron. So both II and III are true and each explains why rain weathers rock.
- ✓ Statement-I Rainwater drives chemical weathering processes such as solution, carbonation, hydration and oxidation.
- ✓ Statement-II Rain dissolves atmospheric carbon dioxide and becomes weakly acidic; this acid dissolves minerals, especially in limestone (carbonation). It explains Statement-I.
- ✓ Statement-III Rain also carries dissolved oxygen, which oxidises iron-bearing minerals and weakens the rock. It too explains Statement-I.
Remember · Chemical weathering needs water plus air — oxygen (oxidation) and carbon dioxide (carbonation). Rainwater brings both.
📘 Read it in NCERT: Class 11 Fundamentals of Physical Geography, Ch 5 (practise this chapter) · Class 11 Fundamentals of Physical Geography, Ch 5 (practise this chapter)
Sources
- NCERT Class 11 · Fundamentals of Physical Geography, Chapter 5 “A group of weathering processes viz; solution, carbonation, hydration, oxidation and reduction act on the rocks to decompose, dissolve or reduce them to a fine clastic state through chemical reactions by oxygen, surface and/or soil water and other acids.”
- NCERT Class 11 · Fundamentals of Physical Geography, Chapter 5 “Water and air (oxygen and carbon dioxide) along with heat must be present to speed up all chemical reactions.”
Question and answer: UPSC's official GS Paper I (2024, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). ·