2024 GS Paper I, all questions

UPSC Prelims 2024 · GS Paper I

Question 7: Geography

Consider the following statements :

  1. Statement-IRainfall is one of the reasons for weathering of rocks.
  2. Statement-IIRain water contains carbon dioxide in solution.
  3. Statement-IIIRain water contains atmospheric oxygen.

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

AnswerUPSC’s answer is (a).

Rain water is slightly acidic because it dissolves carbon dioxide from the air, forming carbonic acid that dissolves limestone and other minerals (carbonation). It also carries dissolved oxygen, which oxidises iron-bearing minerals and weakens rock. Both Statements II and III are correct, and both explain how rainfall weathers rocks. Remember: carbonation, oxidation, hydration and solution are the chemical weathering processes in which water is central.

  • I. Rainfall causes chemical and physical weathering of rocks.
  • II. Dissolved carbon dioxide forms carbonic acid, which attacks rocks (carbonation).
  • III. Dissolved oxygen causes oxidation of minerals such as iron compounds.

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.

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) Right: dissolved carbon dioxide (carbonation) and dissolved oxygen (oxidation) both help rain weather rock.
  • (b) Wrong: both statements explain Statement-I, not only one.
  • (c) Wrong: both Statements II and III are correct.
  • (d) Wrong: rain water does contain dissolved carbon dioxide and oxygen.

Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.

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Source: UPSC, Civil Services (Preliminary) Examination 2024, General Studies Paper I, Series A. The paper on upsc.gov.in.