Science and Technology: UPSC Previous Year Questions (Prelims)
473 previous year UPSC Prelims Science and Technology questions are on this page, from 1996 to 2025, in 21 chapters. Biology: Zoology is the largest, followed by Miscellaneous (energy, vehicles and materials), Botany, Space and ICT. Recent papers lean on applied technology in the news, while older ones lean on school-level physics, chemistry and biology. Filter by chapter to revise one area at a time.
Explanations state facts as of the year each question was asked; words like “recently” refer to that year.
Showing 21–30 of 473 questions
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UPSC 2024Science and Technology · Nuclear Technology
Q21. With reference to radioisotope thermoelectric generators (RTGs), consider the following statements: 1. RTGs are miniature fission reactors. 2. RTGs are used for powering the onboard systems of spacecraft. 3. RTGs can use Plutonium-238, which is a by-product of weapons developments. Which of the statements given above are correct?
Explanation
RTGs are lightweight and compact devices that generate electricity from the heat produced by the natural radioactive decay of isotopes, typically Plutonium-238. They are commonly used in space missions where solar power is insufficient, such as deep-space probes and rovers.
Statement 1 is incorrect: RTGs generate heat through natural radioactive decay, not by controlled nuclear fission, which involves splitting atomic nuclei to release energy. Therefore, they cannot be classified as miniature fission reactors.
Statement 2 is correct: Due to their lightweight, compact design, RTGs have been extensively used in space missions such as Voyager, Curiosity Rover, and Perseverance Rover. They offer a durable and reliable power source, especially for spacecraft operating in deep space, where solar panels are ineffective.
Statement 3 is correct: Plutonium-238 is widely used in RTGs due to its high heat output during decay and low levels of unwanted radiation. While Pu-238 is not naturally occurring, it is mainly produced as a by-product of nuclear weapons development. For example, during the Cold War, it was generated as a by-product of reactions involved in nuclear weapons production.
UPSC 2024Science and Technology · Miscellaneous
Q22. Recently, the term "pumped-storage hydropower" is actually and appropriately discussed in the context of which one of the following?
Explanation
Pumped-storage hydropower (PSH) is primarily discussed in the context of long-duration energy storage. It is a type of hydroelectric power generation that stores excess electricity by pumping water from a lower reservoir to an upper reservoir during times of low energy demand. When energy demand is high, the stored water is released back down through turbines to generate electricity. This technology helps balance grid fluctuations, integrate renewable energy sources like wind and solar, and provide a reliable backup power supply.
UPSC 2024Science and Technology · Miscellaneous
Q23. Which one of the following is the exhaust pipe emission from Fuel Cell Electric Vehicles, powered by hydrogen?
Explanation
The exhaust pipe emission from Fuel Cell Electric Vehicles (FCEVs) powered by hydrogen is water vapour. These vehicles use hydrogen fuel cells to generate electricity through an electrochemical reaction between hydrogen and oxygen. The only by-product of this process is water (H₂O), which is released as vapour, making FCEVs a clean and environmentally friendly transportation option. Fuel cells are unique in terms of the variety of their potential applications; they can use a wide range of fuels and feedstocks and can provide power for systems as large as a utility power station and as small as a laptop computer.
Additional insight:
Working of Hydrogen Fuel Cells Simply put, fuel cells work by combining hydrogen gas (H₂) with oxygen from the air - and the resulting chemical reaction produces electricity. Hydrogen atoms enter the fuel cell at the anode, while oxygen is fed to the cathode. The fuel cell consists of a membrane coated with a catalyst. When the hydrogen molecules hit the catalyst, they’re split into hydrogen ions and electrons. The membrane lets positively charged hydrogen ions pass through, but not the negatively charged electrons, which instead flow through an electric circuit where the electric current is generated. At the cathode side, the hydrogen ions, electrons and the oxygen in the air combine to produce heat. In order to produce enough electricity to be able to propel a vehicle, a complete fuel cell system consists of several hundred membranes stacked together. The fuel cell system is adequate for normal use, but whenever extra power is needed, it’s provided by a battery on the machine. When the fuel cells produce more power than the machine currently needs, the excess energy can be used to charge the battery. The battery is also charged by regenerative braking.
UPSC 2023Science and Technology · Biotechnology
Q24. ‘Aerial metagenomics’ best refers to which one of the following situations?
Explanation
Metagenomics delves into the study of microbes within their native habitats. "Aerial metagenomics" entails collecting air samples from a specific setting to capture the genetic material (DNA) of various microorganisms, encompassing bacteria, viruses, fungi, and other microscopic life forms.
UPSC 2023Science and Technology · Biotechnology
Q25. Microsatellite DNA’ is used in the case of which one of the following?
Explanation
Microsatellite DNA, alternatively known as short tandem repeats (STRs), represents a genetic marker characterised by repetitive sequences of DNA. Highly polymorphic, microsatellites exhibit varying lengths attributed to discrepancies in the number of repeat units. By scrutinising the discrepancies in microsatellite DNA sequences within individuals or populations, scientists can evaluate genetic diversity, population structure, and evolutionary links both within species and across different species.
UPSC 2023Science and Technology · Health
Q26. ‘Wolbachia method’ is sometimes talked about with reference to which one of the following?
Explanation
About the Wolbachia Method Wolbachia is a type of bacterium, that can be introduced into mosquitoes to diminish their capacity for transmitting diseases. Fig: Wolbachia method Wolbachia method is used to control the population of mosquitoes and thus helps in controlling viral diseases such as zika, dengue, and chikungunya spread by the mosquitoes. In this method, the male Aedes Aegypti mosquitoes with Wolbachia mate with wild female mosquitoes that do not have Wolbachia, the eggs will not hatch and thus leads to sterilisation.
UPSC 2023Science and Technology · Nanoscience and Nanotechnology
Q27. Consider the following statements: 1. Carbon fibres are used in the manufacture of components used in automobiles and aircrafts. 2. Carbon fibres, once used, cannot be recycled. Which of the statements given above is/are correct?
Explanation
Statement 1 is correct: Carbon fibre is a material consisting of very thin filaments of carbon atoms. Carbon fibers are fibers characterized by a carbon content of 90% or higher. The principal rationale behind the aerospace industry’s adoption of carbon fiber lies in the weight reduction it offers.
Statement 2 is incorrect: Carbon fibre is environmentally friendly and exhibits a longer life cycle. There are numerous technologies to recycle carbon fibres.
UPSC 2023Science and Technology · Space and Space Technology
Q28. 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?
Explanation
Pair 1 is not correct: Cepheids, also known as Cepheid Variables, are stars that periodically brighten and dim. Due to their behaviour, these objects can function as cosmic indicators, extending their usefulness as yardsticks for distances up to several tens of millions of light-years away, owing to a consistent relationship between their brightness and other factors.
Pair 2 is not correct: A nebula is a very large cloud of gas and dust in outer space. A dead star’s explosion, such as a supernova, releases gas and dust, which in turn forms certain nebulae (more than one nebula). Other nebulae are places where brand-new stars are only starting to develop. It is for this reason that some nebulae are referred to as "star nurseries."
Pair 3 is correct: Pulsars are extremely compact, rapidly km (12 miles). They are virtually entirely made of neutrons that are formed when massive stars run out of fuel and collapse.
UPSC 2023Science and Technology · Space and Space Technology
Q29. Which one of the following countries has its own Satellite Navigation System?
Explanation
The term "Global Navigation Satellite System" (GNSS) encompasses any satellite network offering positioning, navigation, and timing (PNT) services either globally or within specific regions.The Quasi-Zenith Satellite System (QZSS) stands as a regional GNSS owned by the Government of Japan, aiming to bolster coverage in East Asia and Oceania while complementing GPS.
UPSC 2023Science and Technology · Defence Technology
Q30. Consider the following statements: 1. Ballistic missiles are jet-propelled at subsonic speeds throughout their flights, while cruise missiles are rocket-powered only in the initial phase of flight. 2. Agni-V is a medium-range supersonic cruise missile, while BrahMos is a solid - fuelled intercontinental ballistic missile. Which of the statements given above is/are correct?
Explanation
Statement 1 is not correct: Ballistic missiles are rocket-powered only during the initial (boost) phase of flight, following an arcing trajectory to the target after that. Ballistic missiles travel well outside earth’s atmosphere. In contrast, cruise missiles are jet-propelled at subsonic speeds throughout their journeys. Cruise missile flies within the earth’s atmosphere and uses jet engine technology.
Statement 2 is not correct: The Defence Research and Development Organisation (DRDO) of India developed the land-based intercontinental ballistic missile known as Agni-V. The BrahMos is a medium-range Ramjet Supersonic Cruise Missile that may be fired from a submarine, ship, aircraft, or land. The BrahMos is undoubtedly the world’s fastest supersonic cruise missile.
Exam tip:
Content in both statements are interchanged. The term ballistic itself implies launch-arc-fall motion like a can-non shell -- this requires rocket power at least initially, not a jet engine. While, Cruise = implies long "drive-like" flight. Cruise ships, cruise control -- all constant-speed movement. Similarly in S2 too, hence both are likely false.
Answer key for these questions
Q
UPSC year
Correct answer
21
2024
(b) 2 and 3 only
22
2024
(c) Long duration energy storage
23
2024
(d) Water vapour
24
2023
(a) Collecting DNA samples from air in a habitat at one go
25
2023
(a) Studying the evolutionary relationships among various species of fauna
26
2023
(a) Controlling the viral diseases spread by mosquitoes
27
2023
(a) 1 only
28
2023
(a) Only one
29
2023
(d) Japan
30
2023
(d) Neither 1 nor 2
What UPSC has tested in Science and Technology
Recent questions are application-based: electric vehicles, quantum computing, monoclonal antibodies, CRISPR, gravitational waves and space missions.
Older questions test school science: buoyancy, scattering of light, atomic structure and common compounds.
In Physics and Chemistry, explanations that depend on formulas or equations are left out where the original text could not be shown reliably.
The 2025 paper’s Science and Technology questions covered EVs, UAVs, coal gasification, CL-20, Majorana 1, monoclonal antibodies, GAGAN and ISRO missions.
Frequently asked questions
How many previous year UPSC questions are there on Science and Technology?
This page covers 473 previous year UPSC Prelims GS Paper-I questions on Science and Technology, asked from 1996 to 2025. Each has the correct answer and an explanation.
Which Science and Technology chapters have the most questions?
Biology: Zoology has the most with 115 questions, then Miscellaneous with 68, Biology: Botany with 37, Space and Space Technology with 36 and Information and Communication Technology with 32.
How should I revise Science and Technology from these questions?
Take the technology chapters first, because recent papers favour them, then use the Physics, Chemistry and Biology chapters for basics. Each chapter page lists the facts UPSC has tested and has an answer key.
Why do some Chemistry and Physics questions look missing?
Questions whose explanations depend on chemical formulas or equations that could not be shown correctly were left out, rather than risk a wrong formula. The questions that remain have clear explanations in plain words.
