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?
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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