CAPF AC 2025 Q72: Geography – Physical Geography & Geomorphology
Consider the following statements with reference to salt weathering :
1. Salts in rocks expand due to thermal action, hydration and crystallization.
2. Salts like calcium, sodium, magnesium and barium have a tendency to expand.
3. Salt weathering is a typical example of chemical weathering.
Which of the statements given above is/are correct?
- (a) 1 only
- (b) 1 and 2 only
- (c) 2 and 3 only
- (d) 1, 2 and 3
Answer: (b) 1 and 2 only
Explanation
Salt weathering
How to think: salt weathering belongs to physical (mechanical) weathering, because the rock is broken by growing salt crystals and not changed chemically.
| Statement | Fact | Verdict |
|---|---|---|
| 1. Salts in rocks expand due to thermal action, hydration and crystallisation | NCERT states exactly this | Correct |
| 2. Salts such as calcium, sodium, magnesium and barium tend to expand | NCERT lists calcium, sodium, magnesium, potassium and barium; the four named are in that list | Correct |
| 3. Salt weathering is a typical example of chemical weathering | It is a physical weathering process, found in arid and coastal areas | Wrong |
Statements 1 and 2 are correct.
Answer: (b) 1 and 2 only.
Why each option is right or wrong
- (a) Incorrect. Statement 2 is also correct.
- (b) CORRECT. Statements 1 and 2 are right; salt weathering is physical, not chemical.
- (c) Incorrect. Statement 3 is wrong, and statement 1 is left out.
- (d) Incorrect. Statement 3 is wrong because salt weathering is mechanical.
Key point
Physical weathering: frost wedging, thermal expansion, pressure release, salt weathering (crystal growth, hydration, thermal expansion of salts). Chemical weathering: solution, carbonation, hydration, oxidation, reduction.
Remember
Salt weathering: physical, not chemical.
Common mistakes
- Calling salt weathering chemical because salts are chemicals.
- Doubting statement 2 because potassium is not listed in it.
- Mixing the salt hydration (physical) with the hydration of minerals (chemical).
Exam tip
Educated guess: the rock breaks apart as salt crystals grow in cracks, a physical process like frost wedging. That removes statement 3 and leaves (a) or (b); statement 2 repeats the textbook list.
Sources
- NCERT Class XI Fundamentals of Physical Geography, Chapter 6 (Geomorphic Processes: weathering, physical and chemical)
- Savindra Singh, Geomorphology (Prayag Pustak Bhawan), chapter on Weathering