Set D - UPSC Prelims 2025 Solutions

QQuestion

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?

OOptions

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

D) Neither Statement II nor Statement III is correct

✓Correct Answer

C) Only one of the Statements II and III is correct and that explains Statement I

DDalvoy Solutions

Statement I: Correct. Chalk is indeed very permeable (allows water to pass through) while clay is quite impermeable (prevents water movement).

Statement II: Correct and explains Statement I. Chalk is porous with numerous interconnected pore spaces that allow water absorption and movement, making it highly permeable despite being a solid rock.

Statement III: Incorrect. Clay is actually quite porous, but its pores are extremely small (micropores) and poorly connected, which prevents water movement. It's the size and connectivity of pores, not the absence of porosity, that makes clay impermeable.

Only Statement II correctly explains the permeability difference, as chalk's effective porosity allows water flow while clay's microporous structure restricts it.

Solution Diagram for Q<built-in function id>

SUPSC Prelims Strategy and Tips

For rock permeability questions, distinguish between porosity (presence of pores) and permeability (ability for fluids to flow). A rock can be porous but still impermeable if pores are not well-connected.

SUPSC Prelims 2025 Syllabus Analysis

Geography - Rock types and their physical properties

AUPSC Prelims 2025 Question Analysis

Medium to Hard difficulty - requires understanding of rock physics and hydrology concepts

Question 68

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