Prelims PYQs
UPSC CSE PRELIMS 2025 DETAILED ANALYSIS (S&T – Part 1)
Science and Technology (S&T) in the UPSC CSE Prelims tests awareness of recent developments and applications in fields like space, defense, biotechnology, nanotech, robotics, and ICT. Questions emphasize current affairs, especially Indian initiatives (e.g., ISRO missions, DRDO systems), emerging technologies (AI, quantum tech), and their societal relevance. Unlike theory-heavy subjects, S&T focuses on understanding concepts and their applications rather than deep technical details. NCERTs, newspapers, and sources like PIB, DST, and ISRO websites are key. Prioritizing India-specific advancements and linking them to current news ensures relevance. Static portions are minimal but foundational knowledge aids comprehension of dynamic topics.
As regards S&T and Basic Science in CSE Prelims 2025, the questions were reasonable in number. In S&T, questions featured from all the important topics like space sector, defense, IT, biotech and cutting edge technologies. Except for the two basic science questions, all the questions were based on current affairs. Surprisingly, there were two questions related to Electric Vehicles. And the difficulty level of the questions was moderate to difficult.
Given below is the breakdown of the 100 questions asked in CSE Prelims 2025.
The Detailed Analysis of UPSC Prelims 2025 from Science & Technology section are as follows
UPSC Prelims S&T
Q. Consider the following types of vehicles:
I. Full battery electric vehicles
II. Hydrogen fuel cell vehicles
III. Fuel cell-electric hybrid vehicles
How many of the above are considered as alternative powertrain vehicles?
(a) Only one
(b) Only two
(c) All the three
(d) None
Answer: C
Explanation
- A powertrain is the system in a vehicle that generates power and delivers it to the wheels, allowing the vehicle to move. It typically includes the engine, transmission, and drivetrain (including axles, differentials, and drive shafts).
- Cars and buses have powertrains.
- All the three types of vehicles are alternative powertrain vehicles because they use non-conventional propulsion systems compared to traditional internal combustion engines (ICE).
- Full battery electric vehicles (BEVs): These are powered entirely by electricity stored in batteries and use non-ICE systems. Hence option I is correct.
- Hydrogen fuel cell vehicles (FCEVs): Use hydrogen fuel cells to generate electricity to power electric motors. Hence it has an alternative powertrain. Hence option II is correct.
- Fuel cell-electric hybrid vehicles: Combine a fuel cell and a battery or other electric storage system. Thus it is an alternative powertrain. Hence option III is correct.
MOTIVATION, SOURCES AND COVERAGE OF PRELIMS QUESTION IN THE VISIONIAS SOURCES
Motivation: Although the word ‘powertrain’ is not often taken by laymen, alternative energy systems and substitutes for Internal Combustion Engines (ICE) are always in the news. Additionally, the flagging-off of Green Hydrogen Fuel Cell Bus from Kartavya Path, New Delhi in 2023 is one more reason.
Sources:
- https://www.pib.gov.in/PressReleasePage.aspx?PRID=1960481
- https://www.thehindu.com/news/national/indianoil-unveils-indias-first-green-hydrogen-run-bus-that-emits-just-water/article67344306.ece
Coverage of the topic in the VisionIAS Current Affairs Sources
- PT 365 2025 SnT: Article 9.3. Electric Vehicles
- News today (22nd December 2023): Parliamentary Committee submitted report on Promotion of Electric Vehicles (EVs) in the Country
UPSC Prelims S&T
Q. In the context of electric vehicle batteries, consider the following elements:
I. Cobalt
II. Graphite
III. Lithium
IV. Nickel
How many of the above usually make up battery cathodes?
(a) Only one
(b) Only two
(c) Only three
(d) All the four
Answer: C
Explanation
- A lithium-ion battery typically has: a cathode (positive electrode), an anode (negative electrode) and electrolyte.
- Cobalt: It is commonly used in cathodes of batteries like Lithium Cobalt Oxide (LCO), NMC (Nickel Manganese Cobalt), and NCA (Nickel Cobalt Aluminum). Cobalt improves energy density and battery life. Thus option I is correct.
- Graphite: It is used in the anodes, not the cathode. Furthermore, it’s the most common anode material in lithium-ion batteries. This option II is not correct.
- Lithium: It is present in both cathodes and electrolyte. In the cathode, it forms compounds like LiCoO₂, LiFePO₄, LiNiMnCoO₂, etc. Thus option III is correct.
- Nickel: Nickel is used in cathodes like NMC and NCA. Enhances energy density and storage capacity. Thus option IV is correct.
- Hence option (c) is the correct answer.
MOTIVATION, SOURCES AND COVERAGE OF PRELIMS QUESTION IN THE VISIONIAS SOURCES
Motivation: Because batteries and EVs are key to India’s energy security, climate goals, and technological advancement
Sources:
Coverage of the topic in the VisionIAS All India Test Series/ Sandhan/Open Test
Sandhan Vision IAS Prelims Test Series Initiative
Consider the following statements:
1. This is a dark-coloured mineral and is also known by the name plumbago.
2. Tamil Nadu has the highest reserves of this mineral.
3. The mineral is used in Lithium-ion batteries and nuclear reactors.
Which of the following minerals has been described in the statements given above?
(a) Lignite (Brown Coal)
(b) Lead
(c) Graphite
(d) Pyrite (Fool’s Gold)
VisionIAS Current Affairs Source
- PT 365 2025 Science and Technology: 7.2. BATTERY ENERGY STORAGE SYSTEM (BESS)
- News today (23 Apr 2024): South Korean scientists develop sodium ion battery that can be charged in seconds
UPSC Prelims S&T
Q. With reference to Unmanned Aerial Vehicles (UAVs), consider the following statements:
I. All types of UAVs can do vertical landing.
II. All types of UAVs can do automated hovering.
III. All types of UAVs can use batteries only as a source of power supply.
How many of the statements given above are correct?
(a) Only one
(b) Only two
(c) All the three
(d) None
Answer: D
Explanation:
- Unmanned aerial vehicles (UAVs), often referred to as drones, are aircraft that operate without a human pilot on board. They can be controlled remotely or autonomously, and are used for a wide variety of purposes including surveillance, delivery, and even military operations.
- Vertical Landing and Take-Off: Unmanned aerial vehicles (UAVs), often referred to as drones, are aircraft that operate without a human pilot on board. They can be controlled remotely or autonomously, and are used for a wide variety of purposes including surveillance, delivery, and even military operations. A type of drone known as a fixed-wing drone is an aerial vehicle that utilizes rigid wings, a fuselage, tails, a propeller, and a motor to cover long distances at high speeds. Unlike other drones, they cannot hover or land at specific points, requiring a runway or a net for landing. Thus all drones (for example fixed-wing drones) cannot do vertical landing. A fixed-wing drone is an aerial vehicle that utilizes rigid wings, a fuselage, tails, a propeller, and a motor to cover long distances at high speeds. Unlike other drones, they cannot hover or land at specific points, requiring a runway or a net for landing. Thus all drones (like fixed wing drones) cannot do vertical landing. Hence statement I is not correct.
- Automated Hovering: Again, unlike other drones, traditional fixed wing drones cannot hover or land at specific points, requiring a runway or a net for landing. Hence statement II is not correct.
- Battery Usage: UAVs come in many configurations, including: Multirotors (e.g., quadcopters) Fixed-wing UAVs Hybrid VTOLs High-endurance military UAVs (e.g., Predator drones) Many of these cannot rely solely on batteries due to power and endurance limitations. Energy density of batteries is lower than fuel: For long-range UAVs, especially fixed-wing or military UAVs, batteries cannot provide sufficient power or duration. Hence statement III is not correct.
MOTIVATION, SOURCES AND COVERAGE OF PRELIMS QUESTION IN THE VISIONIAS SOURCES
Motivation
- Uses of drones and UAVs have always been in the news; more recently during Operation Sindoor (although this event was too recent to have been taken into consideration)
Sources
- “https://www.thehindu.com/sci-tech/energy-and-environment/watch-demo-of-hydrogen-powered-vertical-take-off-and-landing-aircraft/article68814570.ece
- https://www.thehindu.com/news/national/andhra-pradesh/flying-car-takes-off-guntur-startup-successfully-tests-pilot-less-evtol-prototype/article69372820.ece”
- https://www.sciencedirect.com/topics/computer-science/fixed-wing-drone
- https://www.sciencedirect.com/science/article/abs/pii/S0306261919315107
VisionIAS Current Affairs Source
- Monthly Current Affairs January 2024: Article 4.3. Drones and Security
- News today (10 May 2024): Kamikaze Drones
UPSC Prelims S&T
Q. What is the common characteristic of the chemical substances generally known as CL-20, HMX and LLM-105, which are sometimes talked about in the media?
(a) These are alternatives to hydro-fluorocarbon refrigerants
(b) These are explosives in military weapons
(c) These are high-energy fuels for cruise missiles
(d) These are fuels for rocket propulsion
Answer: B
Explanation:
- CL-20, HMX, and LLM-105 are high-energy explosives, primarily used in military and defense applications. Hence option (b) is the correct answer.
- CL-20 (Hexanitrohexaazaisowurtzitane) is one of the most powerful non-nuclear explosives known to science. Developed in the 1980s by the U.S. Navy CL-20 belongs to a class of cage-structured nitramines.However, it is also extremely sensitive to shock and friction, which limits its widespread deployment and demands highly controlled handling and storage.
- HMX (High Melting Explosive or Octogen) is a widely used nitroamine explosive known for its high detonation velocity and pressure. Chemically more stable than CL-20, HMX is frequently used in military-grade plastic explosives, rocket propellants, and shaped charges. It is more powerful than RDX but less energetic than CL-20.
- LLM-105 (2,6-diamino-3,5-dinitropyrazine-1-oxide) is a newer class of energetic material developed with the goal of enhancing safety without significantly compromising explosive power. Unlike CL-20 and HMX, LLM-105 is classified as an “insensitive high explosive,” meaning it has low sensitivity to shock, heat, or friction, making it much safer for transport and handling.
MOTIVATION, SOURCES AND COVERAGE OF PRELIMS QUESTION IN THE VISIONIAS SOURCES
Motivation:
- SEBEX 2 is based on high-melting explosives (HMX) and was in the news
Sources:
VisionIAS Current Affairs Source
- PT 365 2025 SnT: Article 8.7.1. SEBEX 2
UPSC Prelims S&T
Q. Consider the following statements:
I. It is expected that the Majorana l chip will enable quantum computing.
II. Majorana l chip has been introduced by Amazon Web Services (AWS).
III. Deep learning is a subset of machine learning.
Which of the statements given above are correct?
(a) I and II only
(b) II and III only
(c) I and III only
(d) I, II and III
Answer: C
Explanation:
- Statement I is correct: The Majorana l (Majorana-based) chip refers to an approach using Majorana fermions — exotic quantum particles — for topological quantum computing, which promises greater stability and reduced error rates. This is a research frontier in quantum computing.
- Statement II is not correct: AWS (Amazon Bracket) is working on quantum computing, but the Majorana-based chip is being developed by Microsoft, in collaboration with researchers at Station Q.
- Statement III is correct: Deep learning is a specialized field within machine learning that uses multi-layered neural networks. It’s a subset used for tasks like image recognition, natural language processing, etc.
MOTIVATION, SOURCES AND COVERAGE OF PRELIMS QUESTION IN THE VISIONIAS SOURCES
Motivation:
- Majorana was in the news and extensively covered.
Sources:
- https://www.thehindu.com/sci-tech/technology/microsoft-creates-chip-it-says-shows-quantum-computers-are-years-not-decades-away/article69241156.ece
- https://www.thehindu.com/news/national/tamil-nadu/iit-m-launches-btech-in-ai-and-and-data-analytics-from-this-academic-year/article68289158.ece
VisionIAS All India Test Series/ Sandhan/Open Test:
2025 All India Test Series
Test Code – 4731
Consider the following Pairs:
Quantum Computing Chip Associated Company
1. Ocelot Amazon
2. Majorana 1 Microsoft
3. Sycamore Google
How many of the above are correctly matched with their respective companies?
VisionIAS Current Affairs Source:
- PT 365 2025 Update Part 1: Article 6.2.1.1. Majorana 1
- News today (01 May 2024): Case registered against alleged Deepfake Video of the Union Home Minister in Maharashtra
- (21 Feb 2025): Microsoft launched Majorana 1 Quantum Chip
UPSC Prelims S&T
Q. With reference to monoclonal antibodies, often mentioned in news, consider the following statements:
I. They are man-made proteins.
II. They stimulate immunological function due to their ability to bind to specific antigens.
III. They are used in treating viral infections like that of Nipah virus.
Which of the statements given above are correct?
(a) I and II only
(b) II and III only
(c) I and III only
(d) I, II and III
Answer: D
Explanation:
- Statement I is correct:Monoclonal antibodies (mAbs) are laboratory-engineered proteins that mimic the immune system’s natural ability to fight harmful pathogens. Hence statement I is correct.
- Produced from a single clone of B-cells, they are designed to bind to specific antigens such as those found on viruses, bacteria, or cancer cells. This targeted action allows them to neutralize threats, mark infected or malignant cells for destruction, or block harmful biological processes. Hence statement II is correct.
- mAbs are widely used in treating cancers, autoimmune disorders, and viral infections like COVID-19, Ebola, and Nipah. Their precision makes them powerful tools in both therapy and diagnostics. In India, the monoclonal antibody from Australia has been used on some individuals around the world. Its use was found to be safe. Hence statement III is correct.
MOTIVATION, SOURCES AND COVERAGE OF PRELIMS QUESTION IN THE VISIONIAS SOURCES
Motivation:
- In the context of immune system, many of the cutting-edge developments in biotechnology have been in the news
Sources:
- https://www.thehindu.com/sci-tech/health/nipah-virus-outbreak-kerala-what-are-monoclonal-antibodies/article67330401.ece
- https://www.business-standard.com/health/kerala-s-lab-develops-non-infectious-nipah-virus-like-particles-124060300815_1.html
- https://www.thehindu.com/sci-tech/health/biosimilars-and-the-need-for-a-policy-prescription/article69241369.ece
Sandhan Vision IAS Prelims Test Series Initiative
Consider the following statements regarding monoclonal antibodies:
1. They are artificial antibodies that mimic the activity of our immune systems.
2. They have been used in the treatment of various diseases, including cancer and autoimmune disorders.
Which of the statements given above is/are correct?
(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2
VisionIAS Current Affairs Source
- PT 365 2025 SnT: Article 1.1.7.1. Recombinant Proteins
- Monthly Current Affairs July 2024: Article 7.5.6. Monoclonal Antibodies
- News today (15 July 2024): Monoclonal Antibodies
UPSC Prelims S&T
Q. Consider the following statements:
I. No virus can survive in ocean waters.
II. No virus can infect bacteria.
III. No virus can change the cellular transcriptional activity in host cells.
How many of the statements given above are correct?
(a) Only one
(b) Only two
(c) All the three
(d) None
Answer: D
Explanation:
- Statement I is not correct: Viruses are abundant and active in ocean waters. Marine viruses, particularly bacteriophages (viruses that infect bacteria), are the most numerous biological entities in the ocean. They play a crucial role in regulating microbial populations and nutrient cycles. Studies have shown that viruses can survive in seawater for extended periods, depending on environmental conditions.
- Statement II is not correct: This statement is inaccurate. Bacteriophages, or phages, are viruses that specifically infect and replicate within bacterial cells. They are ubiquitous in environments where bacteria are present, including soil, water, and the human body. Phages play a significant role in controlling bacterial populations and have been explored as alternatives to antibiotics in phage therapy.
- Statement III is not correct: Viruses can and often do alter the transcriptional activity of their host cells. Upon infection, many viruses manipulate the host’s gene expression machinery to favor viral replication and suppress host defenses. For instance, certain viral proteins can interact with host transcription factors, leading to changes in gene expression that facilitate viral propagation
MOTIVATION, SOURCES AND COVERAGE OF PRELIMS QUESTION IN THE VISIONIAS SOURCES
Motivation:
Bacteriophages were in the news during the Mahakumbh Mela
Sources:
- https://www.thehindu.com/news/national/uttar-pradesh/up-govt-quotes-scientist-to-debunk-doubts-about-ganga-waters-purity-at-maha-kumbh/article69245735.ece
- https://www.downtoearth.org.in/science-technology/international-day-for-biological-diversity-2020-why-viruses-are-necessary-71305
- https://pmc.ncbi.nlm.nih.gov/articles/PMC145303/
Sandhan Vision IAS Prelims Test Series Initiative
Consider the following statements regarding Viruses:
1. All viruses contain both RNA and DNA.
2. Bacteriophages (viruses that infect the bacteria) are usually single-stranded DNA viruses
Which of the statements given above is/are correct?
(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2
The remaining content of CSE Prelims 2025 Science & Technology will be featured in separate blog posts.
As can be seen from the above analysis, questions from S&T in CSE Prelims 2025, were a mix of conceptual and factual type. Most of the themes were drawn from the VisionIAS Sandhan Initiative, All India Test Series 2025 and the various components of VisionIAS Current Affairs.
As the importance of the Previous Year Questions (PYQs) cannot be overstated, it is always an indispensable source for every serious aspirant to go ahead with a well–guided strategy.
The VisionIAS 10-year strategy document for S&T is a sought-after source for the PYQ analysis.
TO WATCH THE CSE PRELIMS 2025 ANALYSIS VIDEO, CLICK ON THE FOLLOWING LINK
UPSC Prelims 2025 Analysis | GS Paper 1 – YouTube
TO WATCH THE VISIONIAS 10 Year PYQ ANALYSIS VIDEO, CLICK ON THE FOLLOWING
GS Prelims Analysis / Discussion | 10 Years (2015 – 2024) UPSC PYQ | Science & Technology | Part 2
Further, understand the UPSC Prelims with VisionIAS’s Master Classes on PYQ of UPSC Prelims. This program transforms 13 years of UPSC previous year question papers into a powerful strategy- building resource. Designed to enhance your accuracy, speed, and conceptual clarity, it’s a smart way to turn UPSC PYQs into your strongest preparation tool
