UPSC Prelims 2023 · GS Paper I
Question 56: Science and Technology
Consider the following pairs :
| Objects in space | Description | |
|---|---|---|
| 1. | Cepheids | Giant clouds of dust and gas in space |
| 2. | Nebulae | Stars which brighten and dim periodically |
| 3. | Pulsars | Neutron stars that are formed when massive stars run out of fuel and collapse |
How many of the above pairs are correctly matched?
AnswerUPSC’s answer is (a).
Only pair 3 is correct: pulsars are rapidly rotating neutron stars left when massive stars exhaust their fuel and collapse in a supernova. Cepheids are the stars that brighten and dim periodically (pulsating variables), used to measure cosmic distances; nebulae are giant clouds of dust and gas. In pairs 1 and 2 the descriptions are swapped.
- 1. Cepheids are periodically varying stars, not gas clouds.
- 2. Nebulae are clouds of dust and gas, not pulsating stars.
- 3. Pulsars are neutron stars formed from collapsed massive stars.
How you could have got this
No shortcut here: in a “how many” question, ruling out options doesn’t help. Every statement has to be judged.
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) Correct: only pair 3 is matched correctly.
- (b) Two would need pair 1 or 2 to be right; both are swapped.
- (c) Pairs 1 and 2 have swapped descriptions.
- (d) Pair 3 is right, so not none.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2023, General Studies Paper I, Series A. The paper on upsc.gov.in.