UPSC Prelims 2026 · CSAT
Question 34: Logical Reasoning and Mental Ability
Two identical straight rods are painted in five distinct colours so that each of them gets divided into five equal parts along the length. In one of them, the portions are marked P1, P2, P3, P4 and P5 (not necessarily in that order) whereas in the other, they are marked Q1, Q2, Q3, Q4 and Q5 (not necessarily in that order). When the rods are kept parallel to each other side by side, P1 and Q3 match, P4 matches Q1 or Q2, and Q4 matches P3 or P5. If Q3 and Q5 are adjacent, which of the following is/are possible?
- IQ3 is marked at the middle portion of the straight rod.
- IIP2 is marked at one of the extreme portions of the straight rod.
Select the answer using the code given below.
AnswerUPSC’s answer is (c).
The statements ask only whether an arrangement is possible, so one valid layout each is enough. Number the positions 1 to 5. For I: first rod P4, P2, P1, P5, P3 and second rod Q1, Q2, Q3, Q5, Q4. Then P1 faces Q3, P4 faces Q1, Q4 faces P3, Q3 and Q5 are adjacent, and Q3 is in the middle. For II: first rod P2, P1, P3, P4, P5 and second rod Q1, Q3, Q5, Q2, Q4. Then P1 faces Q3, P4 faces Q2, Q4 faces P5, Q3 and Q5 are adjacent, and P2 is at an extreme end.
- I. Possible: P4, P2, P1, P5, P3 against Q1, Q2, Q3, Q5, Q4 puts Q3 in the middle.
- II. Possible: P2, P1, P3, P4, P5 against Q1, Q3, Q5, Q2, Q4 puts P2 at an end.
How you could have got this
- If you were sure statement I is correct, (b) and (d) go: each of them leaves I out.
What you needed to know: Possible: P4, P2, P1, P5, P3 against Q1, Q2, Q3, Q5, Q4 puts Q3 in the middle.
- Then, if you were sure statement II is correct, (a) goes: it leaves II out.
What you needed to know: Possible: P2, P1, P3, P4, P5 against Q1, Q3, Q5, Q2, Q4 puts P2 at an end.
Only (c) is left. This one needs every statement.
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: II is also possible.
- (b) Wrong: I is also possible.
- (c) Right: a valid layout exists for each.
- (d) Wrong: both layouts satisfy all the conditions.
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.
Source: UPSC, Civil Services (Preliminary) Examination 2026, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.