UPSC CSE 2025 · PYQ · Geomorphology / Rock Properties · hard
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?
Answer
The correct answer is C: Only one of the Statements II and III is correct and that explains Statement I. Chalk is highly permeable because it is porous, allowing water to pass through — so Statement II is correct and explains why chalk is permeable. However, Statement III is incorrect: clay is actually highly porous…
A.Both Statement II and Statement III are correct and both of them explain Statement I
B.Both Statement II and Statement III are correct but only one of them explains Statement I
C.Only one of the Statements II and III is correct and that explains Statement I✓ Correct
D.Neither Statement II nor Statement III is correct
Explanation
Chalk is highly permeable because it is porous, allowing water to pass through — so Statement II is correct and explains why chalk is permeable. However, Statement III is incorrect: clay is actually highly porous (it has many tiny pore spaces holding water), but its pores are so small and poorly connected that water cannot move through it — this makes clay porous but impermeable. So only Statement II is correct and it explains Statement I.
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