Choose the group which is different from the others:
Answer & explanation
Answer: (d) 83, 89, 91, 97
In groups (a), (b) and (c) all four numbers are prime. In group (d), 91 = 7 × 13 is not prime, so that group is the odd one out.
- (a) 17, 37, 47, 97 — all prime.
- (b) 31, 41, 53, 67 — all prime.
- (c) 71, 73, 79, 83 — all prime.
- (d) 83, 89 and 97 are prime, but 91 = 7 × 13. So (d) is different.
Remember · Know the primes up to 100; 91 (7 × 13), 51 (3 × 17) and 87 (3 × 29) are the classic look-alike composites.
Question and answer: UPSC's official GS Paper II (2023, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). ·