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 statements :
- 1. In tropical regions, Zika virus disease is transmitted by the same mosquito that transmits dengue.
- 2. Sexual transmission of Zika virus disease is possible.
Which of the statements given above is/are correct ?
Answer (c) & explanation
Both statements are correct (c). Zika, a flavivirus, is spread mainly by Aedes aegypti (1). This is the same day-biting mosquito that carries dengue, chikungunya and yellow fever, and it breeds in clean, standing water. Zika can also spread sexually (2), through blood transfusion, and from mother to foetus, where it can cause microcephaly (an abnormally small head). The 2015–16 outbreak in Brazil led the WHO to declare a public health emergency of international concern.
India has seen outbreaks in Gujarat (2017), Rajasthan, Kerala and Maharashtra. Notice the control methods, such as source reduction and Wolbachia-infected mosquitoes that cut virus spread. Also remember the different carrier for malaria: the Anopheles mosquito.
Answer as per the official UPSC answer key.
The terms ‘Event Horizon’, ‘Singularity’, ‘String Theory’ and ‘Standard Model’ are sometimes seen in the news in the context of
Answer (a) & explanation
These terms are about understanding the Universe (a). An event horizon is the boundary around a black hole from which nothing, not even light, can escape. A singularity is the point of infinite density at its centre, where general relativity breaks down. String theory tries to unify gravity with quantum physics by treating particles as tiny vibrating strings. The Standard Model describes the fundamental particles and three of the four forces, and its last missing piece, the Higgs boson, was found at CERN in 2012. None of this relates to eclipses (b), satellites (c), or the evolution of life (d).
The Event Horizon Telescope photographed black holes in M87 (2019) and Sagittarius A* (2022). Notice the 2020 Nobel Prize for black-hole research (Penrose, Genzel and Ghez).
Answer as per the official UPSC answer key.
With reference to agriculture in India, how can the technique of ‘genome sequencing’ often seen in the news, be used in the immediate future ?
- 1. Genome sequencing can be used to identify genetic markers for disease resistance and drought tolerance in various crop plants.
- 2. This technique helps in reducing the time required to develop new varieties of crop plants.
- 3. It can be used to decipher the host-pathogen relationships in crops.
Select the correct answer using the code given below :
Answer (d) & explanation
All three are correct (d). Genome sequencing reads an organism's full DNA. In crops, it helps scientists find genetic markers for traits such as disease resistance and drought tolerance (1). These markers drive marker-assisted selection, which can cut years off breeding new varieties (2). Sequencing both the crop and its pathogen shows how infection works, revealing host–pathogen relationships (3) and helping to design resistance.
India helped sequence rice, wheat, tomato and chickpea. Notice the new tools: in 2025, ICAR released the world's first genome-edited rice varieties (DRR Dhan 100 Kamala and Pusa DST Rice 1) using SDN-1/2 editing, which India exempts from GM rules. Pusa Basmati 1509 with blast resistance came from marker-assisted breeding.
Answer as per the official UPSC answer key.
Consider the following pairs :
| Commonly used/consumed materials | Unwanted or controversial chemicals likely to be found in them
| 1. Lipstick | Lead
| 2. Soft drinks | Brominated vegetable oils
| 3. Chinese fast food | Monosodium glutamate
Which of the pairs given above is/are correctly matched ?
Answer (d) & explanation
All three pairs are correct (d). Tests in several countries have found traces of lead in some lipsticks (1), a heavy metal that is toxic even in small doses. Brominated vegetable oil (BVO) was used to keep citrus flavours evenly mixed in soft drinks (2). It is banned in India, the EU and Japan, and the US FDA banned it in 2024 over thyroid concerns. Monosodium glutamate (MSG), sold as Ajinomoto, is the flavour enhancer that gives the umami taste in Chinese fast food (3). It is widely seen as safe but remains controversial.
Notice the related news: the Maggi row of 2015, when FSSAI questioned its MSG labelling and lead levels. Other food additives to know are potassium bromate (banned in bread) and trans fats.
Answer as per the official UPSC answer key.
Organic Light Emitting Diodes (OLEDs) are used to create digital display in many devices. What are the advantages of OLED displays over Liquid Crystal displays ?
- 1. OLED displays can be fabricated on flexible plastic substrates.
- 2. Roll-up displays embedded in clothing can be made using OLEDs.
- 3. Transparent displays are possible using OLEDs.
Select the correct answer using the code given below :
Answer (c) & explanation
All three are correct (c). In an OLED display, each pixel is made of organic compounds that give off their own light, so it needs no backlight. The layers are very thin and can be laid on flexible plastic (1). This makes possible foldable and roll-up screens, including ones built into clothing (2), as well as transparent displays (3). Backlit LCDs cannot do any of these easily. OLEDs also show true blacks and high contrast, because a pixel can switch off fully, and they use less power for dark images.
Their drawbacks are burn-in and a shorter life for blue pixels. Notice the next steps: MicroLED and QD-OLED. Foldable phones and rollable TVs now use flexible OLEDs.
Answer as per the official UPSC answer key.
What is the application of Somatic Cell Nuclear Transfer Technology ?
Answer (c) & explanation
SCNT is used for reproductive cloning of animals (c). In Somatic Cell Nuclear Transfer, the nucleus of a body (somatic) cell is placed into an egg whose own nucleus has been removed. The egg is then made to divide and grows into a genetic copy of the donor. Dolly the sheep (1996, Roslin Institute) was the first mammal cloned this way. In India, NDRI Karnal cloned the buffalo Garima (2010), and India later cloned a Gir calf and cloned camels in Dubai. SCNT has nothing to do with biolarvicides (a), bioplastics (b), or disease-free organisms (d).
It is also used for therapeutic cloning, to make patient-matched stem cells. Notice the ethics: India bans human reproductive cloning under ICMR guidelines.
Answer as per the official UPSC answer key.
In India, it is legally mandatory for which of the following to report on cyber security incidents ?
- 1. Service providers
- 2. Data centres
- 3. Body corporate
Select the correct answer using the code given below :
Answer (d) & explanation
All three must report cyber incidents (d). Under Section 70B of the IT Act, 2000 and the CERT-In Rules, 2013, service providers (1), data centres (2), body corporates (3) and intermediaries must report cyber security incidents to CERT-In (the Indian Computer Emergency Response Team, under MeitY). CERT-In's April 2022 directions set a six-hour reporting deadline. They also require logs to be kept for 180 days, and VPN providers must store user details for five years.
Critical sectors are protected by NCIIPC under Section 70A. Notice the related laws: the Digital Personal Data Protection Act, 2023 and its 2025 Rules, which add a duty to report data breaches to the Data Protection Board.
Answer as per the official UPSC answer key.
India is an important member of the ‘International Thermonuclear Experimental Reactor’. If this experiment succeeds, what is the immediate advantage for India?
Answer (d) & explanation
India could build fusion reactors (d). ITER, being built at Cadarache, France, is testing whether a tokamak can produce net energy from fusion, aiming for ten times more energy out than goes into heating its plasma. As one of seven members (EU, India, China, Japan, Korea, Russia, USA), India gets full access to the know-how in return for its share, including the cryostat built by L&T. Thorium (a) belongs to India's separate three-stage fission programme. Satellite navigation (b) is NavIC's field. ITER does nothing for fission reactors (c).
Fusion joins light nuclei, such as deuterium and tritium, and leaves little long-lived waste. Notice India's own tokamaks, Aditya and SST-1, at the Institute for Plasma Research, Gandhinagar.
Answer as per the official UPSC answer key.
Regarding ‘DigiLocker’, sometimes seen in the news, which of the following statements is/are correct?
- 1. It is a digital locker system offered by the Government under Digital India Programme.
- 2. It allows you to access your e-documents irrespective of your physical location.
Select the correct answer using the code given below.
Answer (c) & explanation
Both statements are correct (c). DigiLocker, launched by MeitY in 2015 under the Digital India programme (1), is a cloud-based document wallet linked to Aadhaar. Agencies such as transport departments, CBSE, universities and UIDAI issue documents into it directly, and users can open them from anywhere (2). Under the IT Rules (2016 amendment), documents in DigiLocker are legally valid like physical originals. Police can accept a digital driving licence and registration certificate under the Motor Vehicles rules.
Today it has hundreds of millions of users and links to ABHA health records and the Academic Bank of Credits. Notice that it is part of India's Digital Public Infrastructure stack, alongside Aadhaar, UPI and e-Sign.
Answer as per the official UPSC answer key.
With reference to ‘Astrosat’, the astronomical observatory launched by India, which of the following statements is/are correct?
- 1. Other than USA and Russia, India is the only country to have launched a similar observatory into space.
- 2. Astrosat is a 2000 kg satellite placed in an orbit at 1650 km above the surface of the Earth.
Select the correct answer using the code given below.
Answer (d) & explanation
Neither statement is correct (d). AstroSat, launched by PSLV-C30 in September 2015, is India's first dedicated multi-wavelength space observatory. It can watch the sky in ultraviolet, visible and X-ray bands at the same time. Statement 1 is wrong because Japan, the European Space Agency and China had also launched space observatories, so India was not the third after the USA and Russia. Statement 2 is wrong because it weighs about 1,513 kg and orbits at about 650 km, not 2,000 kg at 1,650 km.
Its UVIT found extreme-UV light from a distant galaxy (AUDFs01) in 2020. Notice the later Indian science missions: Aditya-L1 (Sun, 2023) and XPoSat (X-ray polarimetry, 2024).
Answer as per the official UPSC answer key.
Consider the following statements :
The Mangalyaan launched by ISRO
- 1. is also called the Mars Orbiter Mission
- 2. made India the second country to have a spacecraft orbit the Mars after USA
- 3. made India the only country to be successful in making its spacecraft orbit the Mars in its very first attempt
Which of the statements given above is/are correct?
Answer (c) & explanation
Statements 1 and 3 are correct (c). Mangalyaan, officially the Mars Orbiter Mission (MOM) (1), was launched by PSLV-C25 in November 2013. It entered Mars orbit on 24 September 2014, making India the first country to succeed on its first attempt (3). Statement 2 is wrong because the USSR, the USA and the European Space Agency had reached Mars orbit earlier. India was the fourth space agency to do it and the first in Asia. It cost about ₹450 crore, less than many Hollywood films.
It was meant to last six months but worked for about eight years, until 2022. Notice the next step, Mangalyaan-2, a planned orbiter, and remember that China's Tianwen-1 (2021) both orbited Mars and landed a rover.
Answer as per the official UPSC answer key.
With reference to ‘LiFi’, recently in the news, which of the following statements is/are correct?
- 1. It uses light as the medium for high-speed data transmission.
- 2. It is a wireless technology and is several times faster than ‘WiFi’.
Select the correct answer using the code given below.
Answer (c) & explanation
Both are correct (c). Li-Fi sends data through LED light that flickers too fast for the eye to see (1). It is wireless, and lab tests have reached speeds many times faster than Wi-Fi (2).
The idea was popularised by Harald Haas in 2011. Because light does not pass through walls, Li-Fi is more secure but limited to one room, and it needs line of sight. It can work where radio waves cause problems, such as aircraft cabins, hospitals and underwater. Notice how the same visible light that lets us see can also carry information.
Answer as per the official UPSC answer key.
In the context of the developments in Bioinformatics, the term ‘transcriptome’, sometimes seen in the news, refers to
Answer (b) & explanation
The transcriptome is the full set of RNA transcripts, mainly mRNA, that an organism or cell expresses at a given time (b). Option (a) is wrong: genome-editing enzymes such as CRISPR-Cas9 are tools, not a transcriptome. Option (c) is wrong because the transcriptome is a set of molecules, not a description of how genes are expressed. Option (d) is wrong because mutations change DNA itself.
Think of the "-omes" in a row: the genome is all the DNA, the transcriptome all the RNA, and the proteome all the proteins. Notice how comparing transcriptomes of healthy and diseased cells reveals which genes are switched on, helping cancer research and crop science.
Answer as per the official UPSC answer key.
‘Project Loon’, sometimes seen in the news, is related to
Answer (b) & explanation
Project Loon was about wireless communication (b). Google's X lab sent solar-powered high-altitude balloons into the stratosphere, about 20 km up, to work as floating cell towers and bring internet access to remote and disaster-hit areas. It had nothing to do with waste management (a), solar power production as such (c), though the balloons used solar panels, or water conservation (d).
Loon helped restore connectivity after floods in Peru and Hurricane Maria in Puerto Rico, but it was shut down in 2021 as too costly. Notice how the same goal of connecting remote places now drives satellite constellations such as Starlink and OneWeb.
Answer as per the official UPSC answer key.
‘Net metering’ is sometimes seen in the news in the context of promoting the
Answer (a) & explanation
Net metering promotes the production and use of solar energy by households and consumers (a). A bidirectional meter records power a rooftop solar owner exports to the grid and power drawn from it, and the consumer pays only for the net amount. It has no link to piped natural gas (b), CNG kits in cars (c) or water meters (d).
Gross metering is different: all solar power is sold to the grid at a fixed tariff. Net metering is central to India's rooftop solar programme, including PM Surya Ghar: Muft Bijli Yojana (2024). Notice how it turns consumers into "prosumers", who both produce and consume power.
Answer as per the official UPSC answer key.
What is ‘Greased Lightning-10 (GL-10)’, recently in the news?
Answer (a) & explanation
GL-10 Greased Lightning was an electric plane tested by NASA (a). This prototype drone had ten propellers driven by battery-electric motors, and its wings and tail tilted, so it could take off vertically like a helicopter and then fly like a plane. It was not a Japanese solar aircraft (b), a Chinese space observatory (c) or an ISRO reusable rocket (d).
NASA tested it in 2015 as part of work on quieter, efficient electric flight. Notice how its idea of distributed electric propulsion now drives the new field of eVTOL air taxis, which several companies, including Indian start-ups, are developing.
Answer as per the official UPSC answer key.
Which of the following statements is/are correct?
Viruses can infect
- 1. bacteria
- 2. fungi
- 3. plants
Select the correct answer using the code given below.
Answer (d) & explanation
All three are correct (d). Viruses can infect every kind of cellular life. Bacteriophages infect bacteria (1). The T4 phage is the classic example, and phages are now being tested as phage therapy against antibiotic-resistant germs. Mycoviruses infect fungi (2), and some are being explored as biocontrol agents. Plant viruses infect plants (3). Tobacco mosaic virus, the first virus ever discovered (Ivanovsky, 1892), is one example, along with banana bunchy top and cotton leaf curl.
Viruses also infect archaea, and even giant viruses can be attacked by virophages. Notice why viruses sit outside the five-kingdom classification: they have no cell machinery of their own. They are inert outside a host and come alive only inside a living cell.
Answer as per the official UPSC answer key.
On which of the following can you find the Bureau of Energy Efficiency Star Label?
- 1. Ceiling fans
- 2. Electric geysers
- 3. Tubular fluorescent lamps
Select the correct answer using the code given below.
Answer (d) & explanation
All three carry the BEE star label (d). The Bureau of Energy Efficiency (a statutory body under the Energy Conservation Act, 2001, under the Ministry of Power) runs the Standards & Labelling programme from 2006. It rates appliances from 1 to 5 stars, with more stars meaning more efficient. Labels are mandatory for items like air conditioners, frost-free refrigerators, tubular fluorescent lamps (3), distribution transformers, electric geysers (2), colour TVs and LED lamps. Ceiling fans (1) were voluntary at first and became mandatory in 2023.
Notice the link with UJALA, which spread cheap LED bulbs, and with the Energy Conservation Building Code. The 2022 amendment to the Act also brought in a domestic carbon credit trading framework.
Answer as per the official UPSC answer key.
In which of the following activities are Indian Remote Sensing (IRS) satellites used?
- 1. Assessment of crop productivity
- 2. Locating groundwater resources
- 3. Mineral exploration
- 4. Telecommunications
- 5. Traffic studies
Select the correct answer using the code given below.
Answer (a) & explanation
IRS satellites, such as Resourcesat, Cartosat and Oceansat, image the earth for crop production forecasts (1), groundwater prospect maps (2) and mineral and geological mapping (3). So the answer is (a). Telecommunication (4) is the job of the GSAT/INSAT series, and UPSC's key does not count traffic studies (5).
IRS data also supports forest mapping, urban planning, disaster monitoring and the FASAL crop forecasting programme. Bhuvan is ISRO's geoportal that shares this data. Notice how India built its space programme around development needs.
Answer as per the official UPSC answer key.
H1N1 virus is sometimes mentioned in the news with reference to which one of the following diseases?
Answer (d) & explanation
H1N1 is the influenza A strain behind the 2009 swine flu pandemic (d), and it has returned in seasonal waves in India. H and N stand for the surface proteins haemagglutinin and neuraminidase. AIDS (a) is caused by HIV, dengue (c) by the dengue virus spread by the Aedes mosquito, and bird flu (b) is usually caused by H5N1.
The 2009 virus mixed genes from pig, bird and human flu viruses, which is why it was called swine flu. Notice how the One Health approach links human, animal and environmental health to prevent such outbreaks.
Answer as per the official UPSC answer key.