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.
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Questions per year, counted from the official papers.
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Consider the following activities :
- 1. Spraying pesticides on a crop field
- 2. Inspecting the craters of active volcanoes
- 3. Collecting breath samples from spouting whales for DNA analysis
At the present level of technology, which of the above activities can be successfully carried out by using drones ?
Answer (d) & explanation
Drones can do all three (d). Drones are used to spray pesticides and fertilisers on crops (1), saving time and reducing farmers' exposure to chemicals. India promotes Kisan drones and the Namo Drone Didi scheme (2023), which gives drones to women's SHGs. Drones fly over active volcanoes to inspect craters and sample gases (2), where it is too dangerous for people. In the SnotBot project, drones collect breath samples from spouting whales (3) for DNA, hormone and health studies, without disturbing them. So any option leaving one out is wrong.
Notice India's drone policy: the liberal Drone Rules, 2021, the PLI scheme for drones, and the ban on most imported drones (2022). Drones were used widely in Operation Sindoor (2025).
Answer as per the official UPSC answer key.
“The experiment will employ a trio of spacecraft flying in formation in the shape of an equilateral triangle that has sides one million kilometres long, with lasers shining between the craft.” The experiment in question refers to
Answer (d) & explanation
The experiment is Evolved LISA (d). The Laser Interferometer Space Antenna, in its evolved form (eLISA), plans three spacecraft flying in an equilateral triangle millions of kilometres on a side, with lasers shining between them. Tiny changes in the distance between them will reveal gravitational waves from sources such as merging giant black holes. LISA Pathfinder (c), launched in 2015, was a single craft that only tested the technology. Voyager-2 (a) is exploring interstellar space. New Horizons (b) flew past Pluto in 2015.
The mission, now just called LISA, was approved by the ESA in January 2024, with launch planned around 2035 and arms of about 2.5 million km. Notice its ground-based cousins: LIGO, Virgo, KAGRA and LIGO-India.
Pathfinder was a test of the technology using one spacecraft. The three-spacecraft triangle is the full mission.
Answer as per the official UPSC answer key.
Consider the following statements :
- 1. Genetic changes can be introduced in the cells that produce eggs or sperms of a prospective parent.
- 2. A person’s genome can be edited before birth at the early embryonic stage.
- 3. Human induced pluripotent stem cells can be injected into the embryo of a pig.
Which of the statements given above is/are correct ?
Answer (d) & explanation
All three statements are correct (d). Gene-editing tools such as CRISPR-Cas9 can change the DNA of germline cells, the cells that make eggs or sperm (1). Such changes would pass to future generations. A person's genome can be edited at the early embryo stage (2), as in the 2018 case of the Chinese scientist He Jiankui, who made the first gene-edited babies and was jailed. Human induced pluripotent stem (iPS) cells, made by reprogramming adult cells, have been injected into pig embryos to make human–pig chimeras (3), for research into growing human organs.
These are all technically possible but ethically debated. Notice the newer step: pig kidneys and hearts, genetically edited, were transplanted into living humans in the USA (2022–25).
Answer as per the official UPSC answer key.
What is the importance of using Pneumococcal Conjugate Vaccines in India ?
- 1. These vaccines are effective against pneumonia as well as meningitis and sepsis.
- 2. Dependence on antibiotics that are not effective against drug-resistant bacteria can be reduced.
- 3. These vaccines have no side effects and cause no allergic reactions.
Select the correct answer using the code given below :
Answer (b) & explanation
Statements 1 and 2 are correct (b). Pneumococcal Conjugate Vaccine (PCV) protects against Streptococcus pneumoniae, a bacterium that causes pneumonia, meningitis and sepsis (1). Pneumonia is a leading killer of young children in India. Statement 2 is right because fewer infections mean less antibiotic use, which slows the spread of drug-resistant bacteria. Statement 3 is wrong because, like every vaccine, PCV can cause side effects such as fever or swelling, and rare allergic reactions.
PCV was added to the Universal Immunisation Programme in 2017 and expanded across India in 2021. Notice India's own PCV, Pneumosil, made by the Serum Institute and approved in 2020. The U-WIN portal (2024) now records every vaccination digitally.
Answer as per the official UPSC answer key.
In India, the term “Public Key Infrastructure” is used in the context of
Answer (a) & explanation
PKI refers to digital security infrastructure (a). Public Key Infrastructure is the system of encryption keys, digital certificates and certifying authorities that makes digital signatures and secure online transactions possible. Each user has a public key, which anyone can see, and a private key, kept secret. A certifying authority vouches that a public key belongs to a particular person. In India, the Controller of Certifying Authorities, under the IT Act, 2000, oversees PKI and runs the Root Certifying Authority of India. It has nothing to do with food (b), health and education (c), or transport (d).
Notice the everyday uses: Aadhaar eSign, income tax filing with digital signatures, e-tendering, and the HTTPS padlock on websites.
Answer as per the official UPSC answer key.
Which of the following statements are correct regarding the general difference between plant and animal cells?
- 1. Plant cells have cellulose cell walls whilst animal cells do not.
- 2. Plant cells do not have plasma membrane unlike animal cells which do.
- 3. Mature plant cell has one large vacuole whilst animal cell has many small vacuoles.
Select the correct answer using the code given below :
Answer (c) & explanation
Statements 1 and 3 are correct (c). Statement 1 is right because plant cells have a rigid cell wall made of cellulose, outside the cell membrane, which gives them shape and support. Animal cells have no cell wall. Statement 3 is right because a mature plant cell usually has one large central vacuole, filled with cell sap, which keeps the cell firm (turgid). Animal cells have only small, temporary vacuoles, or none. Statement 2 is wrong because both plant and animal cells have a plasma membrane. In plants it lies just inside the cell wall and controls what enters and leaves.
Other differences: plant cells have chloroplasts for photosynthesis, while animal cells have centrioles. Notice that fungi have walls of chitin, not cellulose.
Answer as per the official UPSC answer key.
In the context of recent advances in human reproductive technology, “Pronuclear Transfer” is used for
Answer (d) & explanation
Pronuclear transfer prevents mitochondrial diseases (d). Mitochondria have their own small set of DNA, passed on only from the mother. Faults in it cause serious diseases of the muscles, brain and heart. In pronuclear transfer, the egg of the mother is fertilised by the father's sperm. The two pronuclei, holding the parents' main DNA, are moved into a donor egg that has healthy mitochondria and whose own nuclei have been removed. The child gets the parents' genes but healthy mitochondria, hence the term "three-parent babies". It is not normal IVF (a), editing of sperm-making cells (b), or turning stem cells into embryos (c).
The UK legalised the method in 2015. Notice that in 2025, UK doctors reported eight babies born using it.
Answer as per the official UPSC answer key.
In India, why are some nuclear reactors kept under “IAEA Safeguards” while others are not ?
Answer (b) & explanation
Some reactors use imported uranium, others domestic (b). After the 2008 India–US civil nuclear deal and the Nuclear Suppliers Group waiver, India separated its civilian and military facilities. Reactors fuelled by imported uranium (from Russia, Kazakhstan, Canada and others) are placed under IAEA safeguards, so suppliers can check the fuel is not used for weapons. Reactors on domestic uranium and the strategic programme stay outside. Option (a) is wrong because thorium is not the dividing line. Options (c) and (d) are wrong because all Indian power reactors are run by state-owned firms such as NPCIL.
Notice India's three-stage nuclear programme, planned by Homi Bhabha: PHWRs, then fast breeder reactors, then thorium reactors. India is not a member of the NPT.
Answer as per the official UPSC answer key.
With the present state of development, Artificial Intelligence can effectively do which of the following ?
- 1. Bring down electricity consumption in industrial units
- 2. Create meaningful short stories and songs
- 3. Disease diagnosis
- 4. Text-to-Speech Conversion
- 5. Wireless transmission of electrical energy
Select the correct answer using the code given below :
Answer (b) & explanation
AI could do tasks 1, 3 and 4 in UPSC's 2020 key (b). By 2020, AI was already proven at cutting electricity use in industry (1), for example Google's DeepMind cutting data centre cooling energy by about 40%. It could help diagnose diseases (3) from X-rays, scans and eye images. It was widely used for text-to-speech (4). Statement 5 is wrong because wireless power transfer is a matter of physics, not AI. UPSC's key also left out writing meaningful stories and songs (2).
Keep the year in mind: since ChatGPT (late 2022), generative AI can clearly write stories and songs. Notice India's moves: the IndiaAI Mission (2024, ₹10,372 crore), the AI Impact Summit in New Delhi (February 2026) and AI governance guidelines (2025).
This answer reflects 2020. A question set today might count creative writing.
Answer as per the official UPSC answer key.
With reference to solar water pumps, consider the following statements :
- 1. Solar power can be used for running surface pumps and not for submersible pumps.
- 2. Solar power can be used for running centrifugal pumps and not the ones with piston.
Which of the statements given above is/are correct ?
Answer (d) & explanation
Neither statement is correct (d). Statement 1 is wrong: solar panels can run both surface pumps, which lift water from ponds and canals, and submersible pumps, which sit inside a borewell. Statement 2 is wrong: solar power can run both centrifugal pumps and positive-displacement pumps, such as piston pumps. Each statement wrongly rules out one type; the pump type depends on the water depth and flow needed, not on the power source.
Notice PM-KUSUM (2019), which subsidises standalone solar pumps, solarisation of grid-connected pumps, and small solar plants on farmland. Solar pumps cut diesel use and power subsidies, but critics warn that free daytime power can lead to over-extraction of groundwater.
Answer as per the official UPSC answer key.
With reference to Visible Light Communication (VLC) technology, which of the following statements are correct ?
- 1. VLC uses electromagnetic spectrum wavelengths 375 to 780 nm.
- 2. VLC is known as long-range optical wireless communication.
- 3. VLC can transmit large amounts of data faster than Bluetooth.
- 4. VLC has no electromagnetic interference.
Select the correct answer using the code given below :
Answer (c) & explanation
Statements 1, 3 and 4 are correct (c). Visible Light Communication (VLC), also called Li-Fi, sends data by switching LED lights on and off very fast, too fast for the eye to notice. Statement 1 is right because it uses visible light, about 375–780 nm. Statement 3 is right because it can carry large amounts of data faster than Bluetooth, even faster than Wi-Fi in labs. Statement 4 is right because light causes no radio-frequency interference, so it suits hospitals, aircraft and mines. Statement 2 is wrong because light cannot pass through walls, which makes VLC a short-range technology.
Harald Haas coined the term "Li-Fi" in 2011. Notice that the IEEE 802.11bb standard (2023) brought Li-Fi into the Wi-Fi family.
Answer as per the official UPSC answer key.
With reference to “Blockchain Technology”, consider the following statements :
- 1. It is a public ledger that everyone can inspect, but which no single user controls.
- 2. The structure and design of blockchain is such that all the data in it are about cryptocurrency only.
- 3. Applications that depend on basic features of blockchain can be developed without anybody’s permission.
Which of the statements given above is/are correct ?
Answer (d) & explanation
Statements 1 and 3 are correct (d). A blockchain is a distributed ledger: a chain of linked, time-stamped records copied across many computers. Statement 1 is right because a public blockchain can be inspected by anyone, and no single user controls it; changes need agreement across the network. Statement 2 is wrong because it can record any data, such as land titles, supply chains, medical records, voting or certificates, not just cryptocurrency. Statement 3 is right because open, permissionless chains let anyone build applications, such as smart contracts, without asking permission.
Notice India's uses: land records pilots, Vishvasya, the national blockchain framework (2024), and the RBI's e-rupee (CBDC). India taxes crypto gains at 30% but has not banned crypto.
Answer as per the official UPSC answer key.
With reference to carbon nanotubes, consider the following statements :
- 1. They can be used as carriers of drugs and antigens in the human body.
- 2. They can be made into artificial blood capillaries for an injured part of human body.
- 3. They can be used in biochemical sensors.
- 4. Carbon nanotubes are biodegradable.
Which of the statements given above are correct ?
Answer (c) & explanation
Statements 1, 3 and 4 are correct (c). Carbon nanotubes are tiny tubes of carbon atoms, like rolled sheets of graphene. They are very strong, light and good conductors. Statement 1 is right because they are studied as carriers of drugs and antigens (for vaccines) into cells. Statement 3 is right because they are used in biochemical sensors, for example to detect glucose or disease markers. Statement 4 is right because research has shown that enzymes such as myeloperoxidase, found in white blood cells, can break them down. Statement 2 is wrong in UPSC's key, as artificial capillaries made from them are not established.
Notice the concerns: some long nanotubes behave like asbestos in the lungs. Sumio Iijima described them in 1991.
Answer as per the official UPSC answer key.
In the context of wearable technology, which of the following tasks is/are accomplished by wearable devices?
- 1. Location identification of a person
- 2. Sleep monitoring of a person
- 3. Assisting the hearing impaired person
Select the correct answer using the code given below.
Answer (d) & explanation
Wearables do all three tasks (d). Smartwatches and fitness bands use GPS to identify a person's location (1), useful for tracking runs or finding children and elderly people. They monitor sleep using motion sensors and heart-rate sensors (2). Smart hearing aids and earbuds with hearing-assist modes help people with hearing loss (3); for example, some AirPods models were approved as hearing aids in 2024. So any option leaving one out is wrong.
Wearables also measure heart rate, blood oxygen and ECG, and detect falls. Notice the issues: privacy of health data under the DPDP Act, and India's growing home-grown wearable makers such as boAt and Noise, helped by the PLI scheme for electronics.
Answer as per the official UPSC answer key.
‘RNA interference (RNAi)’ technology has gained popularity in the last few years. Why?
- 1. It is used in developing gene silencing therapies.
- 2. It can be used in developing therapies for the treatment of cancer.
- 3. It can be used to develop hormone replacement therapies.
- 4. It can be used to produce crop plants that are resistant to viral pathogens.
Select the correct answer using the code given below.
Answer (a) & explanation
Statements 1, 2 and 4 are correct (a). RNA interference (RNAi) uses small RNA molecules to silence specific genes by destroying their messenger RNA. It is the basis of gene-silencing drugs such as patisiran (1), approved in 2018. It is being tested in cancer therapies to switch off genes that help tumours grow (2). It is used to make virus-resistant crops, such as papaya resistant to ringspot virus (4). Statement 3 is wrong because hormone replacement adds a missing hormone, rather than switching a gene off, so RNAi plays no role.
Fire and Mello won the 2006 Medicine Nobel for discovering RNAi. Notice the related microRNA discovery, which won Ambros and Ruvkun the 2024 Medicine Nobel.
Answer as per the official UPSC answer key.
Recently, scientists observed the merger of giant ‘blackholes’ billions of light-years away from the Earth. What is the significance of this observation?
Answer (b) & explanation
The merger proved gravitational waves exist (b). In September 2015, LIGO in the USA detected gravitational waves, ripples in space-time, from two black holes merging about 1.3 billion light-years away. This confirmed a prediction of Einstein's General Relativity made a century earlier. Weiss, Barish and Thorne won the 2017 Physics Nobel. Option (a) is wrong because the Higgs boson was found at CERN's Large Hadron Collider in 2012. Option (c) is wrong because wormholes remain theoretical. Option (d) is wrong because the observation did not explain the singularity at a black hole's centre.
Notice India's role: LIGO-India, approved in 2023, is being built at Hingoli, Maharashtra. Indian scientists also helped detect the GW250114 signal in 2025.
Answer as per the official UPSC answer key.
Which of the following are the reasons for the occurrence of multi-drug resistance in microbial pathogens in India?
- 1. Genetic predisposition of some people
- 2. Taking incorrect doses of antibiotics to cure diseases
- 3. Using antibiotics in livestock farming
- 4. Multiple chronic diseases in some people
Select the correct answer using the code given below.
Answer (b) & explanation
Statements 2 and 3 are correct (b). Antimicrobial resistance develops in the microbes themselves, when antibiotics kill weak germs and leave the resistant ones to multiply. In India, causes include wrong or incomplete doses of antibiotics (2), easy over-the-counter sales, and heavy antibiotic use in poultry and livestock to boost growth (3). Statements 1 and 4 are wrong because a person's genes or chronic diseases can make infections worse, but they do not make microbes resistant.
Notice India's response: the National Action Plan on AMR (2017, version 2.0 in 2025), the Chennai Declaration, the Red Line campaign on medicine packs, and the ban on colistin as a growth promoter in animals (2019). Kerala was the first state with its own AMR plan.
Answer as per the official UPSC answer key.
For the measurement/estimation of which of the following are satellite images/remote sensing data used?
- 1. Chlorophyll content in the vegetation of a specific location
- 2. Greenhouse gas emissions from rice paddies of a specific location
- 3. Land surface temperatures of a specific location
Select the correct answer using the code given below.
Answer (d) & explanation
Satellites measure all three (d). Chlorophyll in vegetation (1) is estimated from how plants reflect red and near-infrared light, using indices such as NDVI. Healthy leaves reflect more near-infrared. Greenhouse gases such as methane from flooded rice paddies (2) are detected by sensors that measure how these gases absorb sunlight, on satellites such as Sentinel-5P, GOSAT and GHGSat. Land surface temperature (3) is measured using thermal infrared bands, as on Landsat and INSAT-3D. So no option leaving one out is correct.
Notice India's growing role: ISRO's Bhuvan platform, crop yield estimates under FASAL, and the NISAR radar satellite launched with NASA in July 2025.
Answer as per the official UPSC answer key.
What is Cas9 protein that is often mentioned in news?
Answer (a) & explanation
Cas9 is a molecular scissors for gene editing (a). Cas9 is an enzyme found in bacteria, which use it to defend against viruses. A guide RNA leads Cas9 to a matching DNA sequence, where it cuts both strands. Scientists can then remove, fix or add genes. This is the CRISPR-Cas9 system, which won Charpentier and Doudna the 2020 Chemistry Nobel. It is not a biosensor (b), though related Cas proteins are used in tests. It is not a pest-resistance gene (c) like Bt, nor a herbicide (d).
Notice India's uses: the FELUDA COVID test used a related Cas protein, and India released two genome-edited rice varieties in 2025. The USA approved Casgevy, the first CRISPR therapy for sickle cell disease, in 2023.
Answer as per the official UPSC answer key.
Consider the following statements :
- 1. According to the Indian Patents Act, a biological process to create a seed can be patented in India.
- 2. In India, there is no Intellectual Property Appellate Board.
- 3. Plant varieties are not eligible to be patented in India.
Which of the statements given above is/are correct?
Answer (c) & explanation
Only statement 3 is correct (c). Statement 1 is wrong because Section 3(j) of the Patents Act, 1970 excludes plants, animals, seeds, varieties, and essentially biological processes for producing them. Statement 2 was wrong in 2019, because the Intellectual Property Appellate Board (IPAB) existed, set up in 2003. It was abolished only in 2021 by the Tribunals Reforms Act, and its work went to the High Courts. Statement 3 is right because plant varieties cannot be patented. They are protected under the Protection of Plant Varieties and Farmers' Rights (PPV&FR) Act, 2001, a sui generis law allowed by TRIPS.
Notice the PepsiCo case: in 2024, the Delhi High Court upheld the cancellation of its registration for the FL-2027 potato variety, used for Lay's chips.
When an institution has since been abolished, answer from the year the question was set.
Answer as per the official UPSC answer key.