UPSC Prelims 2025 · Question 48 of 100
UPSC Prelims 2025 question on Chalk Permeability
- ExamUPSC CSE
- Year2025
- PaperGeneral Studies Paper I
- SubjectGeography
- TopicGeomorphology
- DifficultyMedium
- TypeAssertion
Consider the following statements:
Statement I:
In the context of effect of water on rocks, chalk is known as a very permeable rock whereas clay is known as quite an impermeable or least permeable rock.
Statement II:
Chalk is porous and hence can absorb water.
Statement III:
Clay is not at all porous.
Which one of the following is correct in respect of the above statements?
Show answer
Answer: C. Only one of the Statements II and III is correct and that explains Statement I
Verdict
Only Statement II is correct and that explains Statement I → Option (c).
Statement by statement
Statement I – CORRECT: Chalk is generally considered a very permeable rock, meaning water can easily pass through it, while clay is known for being quite impermeable or having low permeability, meaning water has difficulty passing through it.
Statement II – CORRECT: Chalk is composed of tiny shells, leaving behind a porous structure with many interconnected spaces. This porous structure allows water to easily seep through the chalk, making it a good aquifer for groundwater storage. Hence Statement II is correct and explains Statement I correctly.
Statement III – INCORRECT: Clay is made of very small, tightly packed particles. While clay has low permeability, it is NOT entirely non-porous — it does have pore spaces but they are very small and not well-connected, making it difficult for water to flow through. This low permeability can lead to water accumulating on top of clay layers. Hence Statement III (claiming clay is 'not at all porous') is not correct.