Science and Technology: previous-year questions
185 real UPSC Prelims questions (2011–2026) with the official answer and a clear explanation. 50 of them came in the last five papers.
How often UPSC asks this
Questions per year, counted from the official papers.
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Attempt the questions
Newest papers first. Tap an option; the answer and the reason appear instantly.
Which one of the following statements is not correct?
Answer (b) & explanation
Option (b) is not correct, so it is the answer. Hepatitis B has had a safe, effective vaccine since the 1980s, and India gives it at birth under the Universal Immunisation Programme. Hepatitis C has no vaccine, but it can now be cured with antiviral drugs. Option (a) is correct because Hepatitis B spreads through blood, sex and from mother to child, much like HIV. Option (c) is correct because about 300 million people live with hepatitis B or C, far more than the roughly 40 million with HIV. Option (d) is correct because both can stay silent for years before causing cirrhosis or liver cancer.
Notice India's National Viral Hepatitis Control Programme (2018) and the WHO goal of eliminating hepatitis by 2030.
Answer as per the official UPSC answer key.
With reference to communication technologies, what is/are the difference/differences between LTE (Long-Term Evolution) and VoLTE (Voice over Long-Term Evolution)?
- 1. LTE is commonly marketed as 3G and VoLTE is commonly marketed as advanced 3G.
- 2. LTE is data-only technology and VoLTE is voice-only technology.
Select the correct answer using the code given below.
Answer (d) & explanation
Neither statement is correct (d). Statement 1 is wrong because LTE, short for Long-Term Evolution, is marketed as 4G, not 3G. VoLTE is a service on that 4G network, not "advanced 3G". Statement 2 is wrong because LTE is mainly for data, but VoLTE carries voice calls as data packets over the same 4G network. So voice and data run together, giving clearer HD voice, faster call set-up, and data use during calls. VoLTE is not voice-only.
India's 4G growth took off when Reliance Jio launched an all-VoLTE network in 2016. Notice the newer steps: 5G rolled out from October 2022, BSNL's indigenous 4G stack went live in 2025, and VoNR carries voice over 5G.
Answer as per the official UPSC answer key.
In the context of digital technologies for entertainment, consider the following statements :
- 1. In Augmented Reality (AR), a simulated environment is created and the physical world is completely shut out.
- 2. In Virtual Reality (VR), images generated from a computer are projected onto real-life objects or surroundings.
- 3. AR allows individuals to be present in the world and improves the experience using the camera of smart-phone or PC.
- 4. VR closes the world, and transposes an individual, providing complete immersion experience.
Which of the statements given above is/are correct?
Answer (b) & explanation
Statements 3 and 4 are correct (b). Statements 1 and 2 swap the definitions. Augmented Reality (AR) keeps you in the real world and adds digital images on top of it, usually through a phone camera or smart glasses (3). Examples are Pokémon Go, Snapchat filters, and apps that show furniture in your room. Virtual Reality (VR) shuts out the real world and places you in a fully simulated one, usually through a headset, giving complete immersion (4).
Mixed reality combines both, letting digital objects interact with the real world, as in Apple Vision Pro. Notice the uses beyond games: training surgeons and pilots, virtual tours of heritage sites, and India's AVGC-XR policy for animation, gaming and extended reality.
Answer as per the official UPSC answer key.
The word ‘Denisovan’ is sometimes mentioned in media in reference to
Answer (b) & explanation
Denisovans are an early human species (b). They are an archaic human species, closely related to the Neanderthals. They were first identified in 2010 from DNA in a finger bone found in Denisova Cave, in Siberia's Altai Mountains. They interbred with modern humans. Traces of their DNA survive in people of Melanesia, Papua New Guinea and parts of Asia. A Denisovan gene, EPAS1, helps Tibetans live at high altitude. They are not dinosaurs (a), a North-East Indian cave (c), or a geological period (d).
Notice the newer finds: a Denisovan jaw from Tibet's Baishiya Cave, and the Harbin skull from China, confirmed as Denisovan in 2025. Svante Pääbo won the 2022 Medicine Nobel for this work.
Answer as per the official UPSC answer key.
With reference to the recent developments in science, which one of the following statements is not correct?
Answer (a) & explanation
Option (a) is the statement that is not correct. Option (b) is correct because scientists can synthesise DNA in the lab, and Craig Venter's team made a bacterium with a fully synthetic genome (2010). Option (c) is correct because the polymerase chain reaction (PCR) copies DNA outside a living cell. Option (d) is correct because plant and animal cells can be grown and made to divide in tissue culture in petri dishes. Recombinant DNA does join genes from different species, but UPSC's key treats building a working chromosome by splicing segments from different species as not possible.
Notice the related news: genome-edited rice varieties released by India in 2025, and synthetic biology research on yeast with synthetic chromosomes (Sc2.0).
Answer as per the official UPSC answer key.
Consider the following statements :
A digital signature is
- 1. an electronic record that identifies the certifying authority issuing it
- 2. used to serve as a proof of identity of an individual to access information or server on Internet
- 3. an electronic method of signing an electronic document and ensuring that the original content is unchanged
Which of the statements given above is/are correct?
Answer (c) & explanation
Only statement 3 is correct (c). A digital signature is an electronic method of signing a document using public-key cryptography. The signer uses a private key, and anyone can check it with the matching public key. It proves who signed and shows the content has not been changed (3). Statement 1 is wrong because the record that identifies the certifying authority is the digital signature certificate, not the signature itself. Statement 2 is wrong because identity for logging in to a server is proved by certificates, passwords and logins, not a digital signature as such.
In India, digital signatures are legally valid under the IT Act, 2000. The Controller of Certifying Authorities licenses issuers. Notice Aadhaar-based eSign and DigiLocker, used widely for e-governance.
Do not confuse the signature with the certificate. Statements 1 and 2 describe what a certificate does.
Answer as per the official UPSC answer key.
When the alarm of your smartphone rings in the morning, you wake up and tap it to stop the alarm which causes your geyser to be switched on automatically. The smart mirror in your bathroom shows the day’s weather and also indicates the level of water in your overhead tank. After you take some groceries from your refrigerator for making breakfast, it recognises the shortage of stock in it and places an order for the supply of fresh grocery items. When you step out of your house and lock the door, all lights, fans, geysers and AC machines get switched off automatically. On your way to office, your car warns you about traffic congestion ahead and suggests an alternative route, and if you are late for a meeting, it sends a message to your office accordingly. In the context of emerging communication technologies, which one of the following terms best applies to the above scenario ?
Answer (b) & explanation
The scenario describes the Internet of Things (b). The IoT is a network of everyday objects fitted with sensors, software and internet links, which collect data, talk to each other and act on their own. The alarm that switches on the geyser, the smart mirror, the fridge that orders groceries, the door lock that turns off appliances, and the car that suggests routes are all IoT devices. Border Gateway Protocol (a) routes traffic between large networks on the internet. Internet Protocol (c) addresses and delivers data packets. A VPN (d) creates a secure, encrypted tunnel.
Notice why IoT is growing: 5G supports huge numbers of linked devices with low delay. It powers smart cities, smart meters and precision farming, but raises privacy and security concerns.
Answer as per the official UPSC answer key.
With reference to solar power production in India, consider the following statements :
- 1. India is the third largest in the world in the manufacture of silicon wafers used in photovoltaic units.
- 2. The solar power tariffs are determined by the Solar Energy Corporation of India.
Which of the statements given above is/are correct ?
Answer (d) & explanation
Neither statement is correct (d). Statement 1 is wrong because, in 2018, India made almost no silicon wafers. It imported most cells and modules, mainly from China, and only assembled modules at home. Statement 2 is wrong because solar tariffs are set by competitive bidding (reverse auctions) or by electricity regulators, the CERC and SERCs. SECI only runs the auctions and acts as an intermediary buyer; it does not fix tariffs.
Notice the change since then: the PLI scheme for high-efficiency solar modules supports building the full chain, from polysilicon to wafers to modules. ALMM lists and import duties favour local makers. India crossed about 100 GW of solar capacity in 2025, aiming for 500 GW of non-fossil capacity by 2030.
Answer as per the official UPSC answer key.
Which of the following leaf modifications occur(s) in the desert areas to inhibit water loss ?
- 1. Hard and waxy leaves
- 2. Tiny leaves
- 3. Thorns instead of leaves
Select the correct answer using the code given below :
Answer (d) & explanation
All three are desert adaptations (d). Desert plants, called xerophytes, cut water loss in several ways. They have hard, waxy leaves with a thick cuticle that reduces evaporation (1), as in Calotropis (aak). They have tiny leaves with fewer, often sunken, stomata (2), as in Acacia and Prosopis (khejri). In some plants, leaves turn into spines or thorns (3), as in cacti and Opuntia, where the green, fleshy stem takes over photosynthesis.
Many desert plants also use CAM photosynthesis, opening their stomata only at night, and they have very deep roots. Notice the opposite case: hydrophytes such as lotus and water hyacinth have stomata on the upper leaf surface and air spaces for floating.
Answer as per the official UPSC answer key.
“3D printing” has applications in which of the following ?
- 1. Preparation of confectionery items
- 2. Manufacture of bionic ears
- 3. Automotive industry
- 4. Reconstructive surgeries
- 5. Data processing technologies
Select the correct answer using the code given below :
Answer (d) & explanation
All five are applications in the official key (d). 3D printing, or additive manufacturing, builds objects layer by layer from a digital design, instead of cutting them out of a block. It can print chocolate and sugar shapes for confectionery (1). Researchers have printed bionic ears that combine living cells with electronics (2). The automotive industry uses it for prototypes and light parts (3). Surgeons use custom-printed implants, bone and skull parts for reconstructive surgery (4). The key also counts data processing technologies (5), since printing depends on CAD and data handling.
Notice India's push: the National Strategy for Additive Manufacturing (2022), printed rocket engine parts by ISRO and Agnikul, and India's first 3D-printed post office in Bengaluru (2023).
Answer as per the official UPSC answer key.
The identity platform ‘Aadhaar’ provides open “Application Programming Interfaces (APIs)”. What does it imply ?
- 1. It can be integrated into any electronic device.
- 2. Online authentication using iris is possible.
Select the correct answer using the code given below :
Answer (c) & explanation
Both statements are correct (c). Aadhaar's open APIs let developers build Aadhaar authentication into any app or electronic device, such as phones, tablets, micro-ATMs and PoS machines (1). Authentication can be done using OTP, fingerprint, face or iris (2). This is why iris scanners work for elderly people with worn fingerprints. These open APIs are part of the "India Stack", along with eKYC, eSign, DigiLocker and UPI.
Face authentication is now widely used, including for pensioners' Jeevan Pramaan life certificates. Notice that India offers this Digital Public Infrastructure model to other countries through MOSIP and the G20's DPI framework (2023).
Answer as per the official UPSC answer key.
With reference to India’s satellite launch vehicles, consider the following statements :
- 1. PSLVs launch the satellites useful for Earth resources monitoring whereas GSLVs are designed mainly to launch communication satellites.
- 2. Satellites launched by PSLV appear to remain permanently fixed in the same position in the sky, as viewed from a particular location on Earth.
- 3. GSLV Mk III is a four-staged launch vehicle with the first and third stages using solid rocket motors; and the second and fourth stages using liquid rocket engines.
Which of the statements given above is/are correct ?
Answer (a) & explanation
Only statement 1 is correct (a). The PSLV mainly launches earth-observation and remote-sensing satellites into sun-synchronous polar orbits. The GSLV carries heavier communication satellites to geosynchronous transfer orbit (1). Statement 2 is wrong because only satellites in geostationary orbit seem fixed in the sky, and those are not PSLV's usual payload. Statement 3 is wrong because GSLV Mk III, now called LVM3, has three stages: two solid strap-on boosters (S200), a liquid core stage (L110) and a cryogenic upper stage (C25).
LVM3 launched Chandrayaan-3 (2023), which landed near the Moon's south pole, and the OneWeb satellites. Notice the human-rated HRLV version is planned for Gaganyaan, with uncrewed test flights first.
Answer as per the official UPSC answer key.
Which of the following is/are the aim/aims of ‘Digital India’ Plan of the Government of India ?
- 1. Formation of India’s own Internet companies like China did.
- 2. Establish a policy framework to encourage overseas multinational corporations that collect Big Data to build their large data centres within our national geographical boundaries.
- 3. Connect many of our villages to the Internet and bring Wi-Fi to many of our schools, public places and major tourist centres.
Select the correct answer using the code given below :
Answer (b) & explanation
Only statement 3 is correct (b). Digital India, launched in July 2015, has three vision areas: digital infrastructure as a basic utility for every citizen, governance and services on demand, and digital empowerment of citizens. Connecting villages through BharatNet broadband and bringing public Wi-Fi to schools, public places and tourist spots fits the first area (3). Creating Chinese-style national internet giants (1) and forcing foreign firms to localise their data centres (2) were not among its stated aims.
Its nine pillars include broadband highways, universal mobile access, e-Kranti and electronics manufacturing. Notice where data localisation came in later: the RBI's 2018 rule on payment data and the DPDP Act, 2023, which allows cross-border transfers except to blacklisted countries.
Answer as per the official UPSC answer key.
In which of the following areas can GPS technology be used ?
- 1. Mobile phone operations
- 2. Banking operations
- 3. Controlling the power grids
Select the correct answer using the code given below :
Answer (d) & explanation
All three use GPS (d). People think of GPS only as a map tool, but each satellite carries atomic clocks, so GPS also gives very accurate time. Mobile networks use GPS time to keep towers in sync so calls hand over smoothly (1). Banks and stock exchanges use it to time-stamp transactions, and ATMs and card systems rely on correct time (2). Power grids use GPS-timed phasor measurement units to compare voltage and current across far-off stations and keep the grid stable (3). So no option that leaves one out is correct.
Notice the security angle: depending on a foreign system is risky. That is why India built NavIC, and is pushing its use in phones, fishing boats and vehicle trackers.
Answer as per the official UPSC answer key.
The terms ‘WannaCry, Petya and EternalBlue’ sometimes mentioned in the news recently are related to
Answer (c) & explanation
These terms relate to cyber attacks (c). EternalBlue was a Windows hacking tool built by the US NSA, which a group called the Shadow Brokers leaked in 2017. WannaCry (May 2017) used it to spread ransomware that locked files and demanded Bitcoin, hitting over 200,000 computers in 150 countries, including UK hospitals and some Indian systems. Petya/NotPetya (June 2017) struck Ukraine and global firms. They have nothing to do with exoplanets (a) or mini satellites (d). Bitcoin was only the ransom method, so (b) is a trap.
Notice India's cyber set-up: CERT-In handles incidents and requires reporting within 6 hours, while NCIIPC protects critical infrastructure. The AIIMS Delhi ransomware attack (2022) showed the risk is real.
Answer as per the official UPSC answer key.
With reference to the Indian Regional Navigation Satellite System (IRNSS), consider the following statements :
- 1. IRNSS has three satellites in geostationary and four satellites in geosynchronous orbits.
- 2. IRNSS covers entire India and about 5500 sq. km beyond its borders.
- 3. India will have its own satellite navigation system with full global coverage by the middle of 2019.
Which of the statements given above is/are correct ?
Answer (a) & explanation
Only statement 1 is correct (a). IRNSS, now called NavIC, was designed with seven satellites: three in geostationary orbit and four in inclined geosynchronous orbit. Statement 2 is wrong because it covers India and a region up to about 1,500 km beyond its borders. "5,500 sq. km" is a tiny area and a deliberate trap. Statement 3 is wrong because NavIC is a regional system, and no global coverage was planned for 2019.
Notice the newer story: the NVS series of second-generation satellites began with NVS-01 (2023), which carries an Indian-made atomic clock. NVS-02 (2025) failed to reach its planned orbit. NavIC also has the global backing of 3GPP for use in mobile phones.
Answer as per the official UPSC answer key.
Consider the following phenomena :
- 1. Light is affected by gravity.
- 2. The Universe is constantly expanding.
- 3. Matter warps its surrounding space-time.
Which of the above is/are the prediction/predictions of Albert Einstein’s General Theory of Relativity, often discussed in media ?
Answer (d) & explanation
All three are predictions of general relativity (d). Einstein's General Theory of Relativity (1915) says that mass and energy curve space-time (3), and that this curve is what we feel as gravity. So light bends as it passes a massive body (1). This was confirmed by Eddington during the 1919 solar eclipse, and it causes gravitational lensing. The theory's equations also describe a universe that is not fixed but expanding (2). Einstein first resisted this, but Hubble observed it in 1929. So options that leave one out are incomplete.
Notice the news links: LIGO detected gravitational waves in 2015, and India is building LIGO-India at Hingoli, Maharashtra. Also, GPS clocks must correct for relativity.
Answer as per the official UPSC answer key.
With reference to the Genetically Modified mustard (GM mustard) developed in India, consider the following statements :
- 1. GM mustard has the genes of a soil bacterium that give the plant the property of pest-resistance to a wide variety of pests.
- 2. GM mustard has the genes that allow the plant cross-pollination and hybridization.
- 3. GM mustard has been developed jointly by the IARI and Punjab Agricultural University.
Which of the statements given above is/are correct ?
Answer (b) & explanation
Only statement 2 is correct (b). GM mustard DMH-11 carries the barnase–barstar genes from a soil bacterium, Bacillus amyloliquefaciens. Barnase makes one parent line male-sterile, and barstar restores fertility in the cross, allowing hybrid seed production (2). A third gene, bar, gives herbicide tolerance. Statement 1 is wrong because it does not give pest resistance; that is Bt technology, as in Bt cotton. Statement 3 is wrong because it was developed by Delhi University's Centre for Genetic Manipulation of Crop Plants under Deepak Pental, not IARI and PAU.
The GEAC approved its environmental release in October 2022. Notice the Supreme Court's split verdict (July 2024), which asked the Centre to frame a national GM crops policy.
The genes do come from a soil bacterium, but they are for hybridisation, not pest resistance.
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Answer as per the official UPSC answer key.
Consider the following pairs :
| Terms sometimes seen in news | Context/Topic
| 1. Belle II experiment | Artificial Intelligence
| 2. Blockchain technology | Digital/Cryptocurrency
| 3. CRISPR-Cas9 | Particle Physics
Which of the pairs given above is/are correctly matched ?
Answer (b) & explanation
Only pair 2 is correct (b). Pair 1 is wrong because Belle II is a particle physics experiment at Japan's SuperKEKB collider (KEK). It studies B-mesons to look for new physics and the matter–antimatter imbalance, and Indian institutions take part. Pair 2 is right because blockchain, a shared, tamper-proof digital ledger, underlies cryptocurrencies such as Bitcoin. Pair 3 is wrong because CRISPR-Cas9 is a gene-editing tool that cuts DNA at a chosen spot, not particle physics.
Notice the news links: Doudna and Charpentier won the Chemistry Nobel (2020) for CRISPR. India released genome-edited rice varieties (2025). The RBI's e-rupee (CBDC) draws on similar ledger ideas, while India taxes crypto gains at 30%.
Answer as per the official UPSC answer key.
What is the purpose of ‘evolved Laser Interferometer Space Antenna (eLISA)’ project ?
Answer (b) & explanation
eLISA is meant to detect gravitational waves (b). The evolved Laser Interferometer Space Antenna, now just LISA, is a European Space Agency mission, with NASA as a partner, planned for launch in the mid-2030s. It will use three spacecraft about 2.5 million km apart, linked by lasers, to pick up low-frequency gravitational waves from merging supermassive black holes. Ground-based LIGO, which first detected gravitational waves in 2015 (Nobel 2017), cannot sense these. Neutrinos (a) are studied by detectors like IceCube and the proposed INO. Missile defence (c) and solar flares (d) are unrelated.
Gravitational waves were predicted by Einstein in 1916. Notice LIGO-India at Hingoli, Maharashtra, approved in 2023, which will join the global detector network.
Answer as per the official UPSC answer key.