SSC CGL 2025 Tier-I · 12 September 2025, Shift 1 · General Intelligence and Reasoning · Question 18 of 100

Text as printed on a candidate's response sheet for this shift; answer per SSC's tentative key as marked on that sheet. Solution last reviewed 11 September 2026.

Where this paper and its answers come from

SSC does not publish CGL question papers or a public answer key. From 2025 the candidate response sheet prints every question and option as a picture, so the text here is transcribed from those pictures for this shift and checked against them independently; where the layout carries meaning, the picture is shown as well. Each answer is the key SSC colour-marked on that sheet. SSC released a tentative key for challenge and later its final one, both only to candidates behind a login, and the sheet does not say which of the two it carries. The solutions are written by UnlockIAS.

Which of the following is the odd one out?

(a)2, 3, 5
(b)11, 13, 17
(c)4, 6, 8
(d)7, 19, 23

Answer

Why

Correct — C. Rule: three of the groups are made entirely of prime numbers.

2, 3, 5 — all prime.
11, 13, 17 — all prime.
7, 19, 23 — all prime.

4, 6 and 8 are even and greater than 2, so each is divisible by 2 and none is prime. That group breaks the rule — option (c).

Why the others are wrong

(a)
2, 3, 5 — 2, 3 and 5 are all prime. 2 is even, which can make this group look like the odd one, but 2 is prime, so the group fits.
(b)
11, 13, 17 — 11, 13 and 17 are all prime, each divisible only by 1 and itself, so this group belongs with the three that are alike.
(d)
7, 19, 23 — 7, 19 and 23 are all prime. They are not consecutive primes, since 11, 13 and 17 are skipped, but that rule rejects 4, 6, 8 too, so it cannot isolate one group.

Concept

An odd-one-out set is decided by a property that three groups share and one lacks. Test the simplest number properties first: even or odd, prime or composite, square or cube.

Here primality splits the options cleanly. Every number in three groups is prime, and no number in 4, 6, 8 is.

A candidate rule must leave exactly one group out. Checking that is what separates the intended rule from a coincidence.

7, 19, 23 is the prime group whose members are not consecutive primes, which can make it look like the answer. That rule fails 4, 6, 8 as well, so it separates two groups, not one, and cannot be the test.

Key facts

2 is the smallest prime and the one even prime.
4 = 2 × 2, 6 = 2 × 3 and 8 = 2 × 2 × 2, so all three are composite.
2, 3, 5 and 11, 13, 17 are runs of consecutive primes, while 7, 19, 23 skips 11, 13 and 17.

Study next

Odd-one-out on number pairs where every number is prime and the gap decidesSquares, cubes and primes below 100 as recognisable sets

Common traps

Picking 2, 3, 5 because it contains an even number.
Picking 7, 19, 23 as the non-consecutive group without checking whether that rule isolates a single group.

13 Sep 2024, 12:30, Reasoning Q.15 takes this a step further: all eight numbers are prime, and the pair of consecutive primes, 73 and 79, is the odd one.

12 Sep 2025, 09:00, Reasoning Q.17 plants 20 in a list of primes.

Related PYQs

No directly related past PYQ was found.

Topic: Semantic Classification — all 18 SSC CGL questions on it, every solved shift.