UPSC Prelims 2026 · CSAT
Question 36: Logical Reasoning and Mental Ability
There are four statements X, Y, Z and W. Their relations are as follows : If X is incorrect, then so is Z; if Y is incorrect, then W is correct; if W is correct, then X is incorrect. Which of the following is/are correct?
- IIf X is correct, then so is Y.
- IIIf Z is correct, then it is not necessary that Y is correct.
Select the answer using the code given below.
AnswerUPSC’s answer is (a).
Translate the rules: not-X leads to not-Z (so Z leads to X); not-Y leads to W; W leads to not-X (so X leads to not-W). For I: if X is correct, W is not correct, and then Y cannot be incorrect (that would make W correct), so Y is correct. I holds. For II: if Z is correct, then X is correct, and by the same chain Y is correct, so Y's truth is necessary, not optional. II is false.
- I. X correct makes W incorrect, which forces Y to be correct.
- II. Z correct forces X, then Y, so Y's correctness is necessary.
How you could have got this
- If you were sure statement I is not correct, (b) and (d) go: each of them leaves I out.
- Then, if you were sure statement II is correct, (c) goes: it includes II.
Only (a) 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) Right: I follows from the rules; II does not.
- (b) Wrong: II is false, since Z forces X and then Y.
- (c) Wrong: II is false.
- (d) Wrong: I is true.
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.