2026 GS Paper I, all questions

UPSC Prelims 2026 · GS Paper I

Question 11: Geography

Consider the following assertion : In the Pleistocene period either the Yamuna once flowed into the Indus, or the Sutlej flowed into the Yamuna and one major tributary of either had shifted from the Ganga to the Indus or vice versa. Which of the following is/are the basis of the above assertion ?

  1. 1.The Nadi-Sukta of the Rigveda
  2. 2.The explorations of the Sutlej and the Yamuna by Robert Bruce Foote
  3. 3.The presence of the same species of dolphins in both the Indus and the Ganga river systems

Select the answer using the code given below :

a1 only
b2 only
c1 and 2
d3

AnswerUPSC’s answer is (d).

The assertion is about a shift in river courses that once linked the Indus and Ganga systems. The biological basis is that the Indus and Ganges river dolphins, closely related and long classed as one species, live in both systems, which is hard to explain unless a shifting tributary such as the Yamuna or Sutlej once connected the basins. The Nadi-Sukta of the Rigveda only lists rivers, and Robert Bruce Foote was a geologist known for prehistoric sites in peninsular India, not for exploring these rivers.

  • 1. The Nadi-Sukta lists rivers; it says nothing about Pleistocene drainage shifts.
  • 2. Foote's work was on prehistory of peninsular India.
  • 3. Dolphins common to the Indus and Ganga imply the systems were once linked.

How you could have got this

  1. If you were sure statement 3 is correct, (a), (b) and (c) go: each of them leaves 3 out.

    What you needed to know: Dolphins common to the Indus and Ganga imply the systems were once linked.

Only (d) is left. You didn’t need statements 1 or 2.

This follows UPSC’s provisional key; the final key could change it.

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: the Nadi-Sukta names rivers of the Rigvedic world but gives no Pleistocene evidence.
  • (b) Wrong: Foote is known for prehistoric finds in peninsular India, not for this explanation.
  • (c) Wrong: neither 1 nor 2 forms the basis of the assertion.
  • (d) Right: shared dolphin species in both river systems point to an old connection.

Only the provisional key (27 May 2026) was found; the final key replaces it when found.

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

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Source: UPSC, Civil Services (Preliminary) Examination 2026, General Studies Paper I, Series A. The paper on upsc.gov.in.