2025 GS Paper I, all questions

UPSC Prelims 2025 · GS Paper I

Question 28: Geography

Consider the following statements :

  1. Statement IIn 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.
  2. Statement IIChalk is porous and hence can absorb water.
  3. Statement IIIClay is not at all porous.

Which one of the following is correct in respect of the above statements?

aBoth Statement II and Statement III are correct and both of them explain Statement I
bBoth Statement II and Statement III are correct but only one of them explains Statement I
cOnly one of the Statements II and III is correct and that explains Statement I
dNeither Statement II nor Statement III is correct

AnswerThe answer is (c).

Chalk is porous and its pores connect, so it absorbs water and lets it pass through: it is permeable. Clay is also porous, in fact highly so, but its pores are tiny and poorly connected, so water cannot move through it easily and it is impermeable. Statement III, that clay is not at all porous, is therefore wrong, while Statement II is right and explains why chalk is permeable. Remember: porosity is storage, permeability is passage.

  • I. Chalk is permeable and clay is impermeable.
  • II. Chalk is porous, so it absorbs water; this explains Statement I.
  • III. Clay is porous but its pores are too small to let water through.

How you could have got this

No shortcut here: in a “how many” question, ruling out options doesn’t help. Every statement has to be judged.

The red flag in Statement III is “all”. In UPSC’s papers, statements with “all” were true 41% of the time (76 statements). A hint, not a rule.

This follows an unofficial answer: UPSC has not published its key for this year, and if that answer is wrong, so is this path.

Which options go is worked out from UPSC’s key and the options, not by a model.

Why each option is right or wrong
  • (a) Wrong: Statement III is incorrect, since clay is porous.
  • (b) Wrong: Statement III is incorrect, so not both are correct.
  • (c) Right: only Statement II is correct, and it explains why chalk is permeable.
  • (d) Wrong: Statement II is correct.

Explanation: written by UPSC Grade, not by UPSC.

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Source: UPSC, Civil Services (Preliminary) Examination 2025, General Studies Paper I, Series A. The paper on upsc.gov.in.