Science and Technology: UPSC Previous Year Questions (Prelims)

Explanation

Alternative Powertrain Vehicles: Vehicles using propulsion systems other than conventional petrol or diesel internal combustion engines (ICEs), focusing on sustainable transport via electricity, hydrogen, or hybrid systems. Full Battery Electric Vehicles (BEVs): Powered solely by electricity in rechargeable battery packs, using electric motors, no ICE, fuel tank, or exhaust. Key Features:

Zero tailpipe emissions, reducing environmental impact. Efficiency depends on electricity source (renewable vs. fossil fuels). Examples: Tesla Model 3 (2017), Tata Nexon EV (2020). Hydrogen Fuel Cell Vehicles (FCEVs): They generate electricity via hydrogen-oxygen electrochemical reaction in fuel cell stack, powering electric motors; emit water vapor, heat. Key Features:

Zero-emission, suited for long-range, heavy-duty applications with fast refueling. Examples: Toyota Mirai (2014), Hyundai Nexo (2018). Fuel Cell Electric Hybrid Vehicles (FCE-HVs): They integrate hydrogen fuel cells and rechargeable batteries to power electric motors, using regenerative braking (turns kinetic energy into electricity by reversing the process that drives the car forward.) Key Features:

Combine fuel cell range, battery power for efficiency. Examples: Toyota, Honda prototypes (2020s). Hence, option (c) is correct.

Explanation

Statement 1 is incorrect: Only Vertical Takeoff and Landing (VTOL) UAVs, like multi-rotor drones (e.g., DJI Phantom, Skydio quadcopters/hexacopters, 2014) and certain hybrid tilt-rotor drones, can land vertically. Fixed-wing UAVs (e.g., NASA Global Hawk, MQ-1 Predator, Wing Loong, 1994) require runways, catapults, or recovery systems (e.g., net, parachute) and cannot land vertically. Hybrid UAVs vary by design. Fixed-wing UAVs excel in energy efficiency, endurance, and speed, ideal for surveillance and long-range missions, unlike multi-rotor drones suited for precision tasks.

Statement 2 is incorrect: Only rotary-wing and multi-rotor UAVs (e.g., DJI Phantom, Skydio, 2014) hover, using vertical thrust from propellers with GPS/stabilization systems can do automated hovering. Fixed-wing UAVs (e.g., MQ-9 Reaper, Global Hawk, 2001) require forward motion for lift and cannot hover. Some VTOL-capable fixed-wing UAVs (e.g., tilt-rotor) can hover, but not universally. Hovering suits aerial photography, surveillance, delivery, and rescue.

Statement 3 is incorrect: UAVs use diverse power sources: batteries (Lithium-ion/LiPo for small/medium multi-rotor drones, e.g., DJI Mavic Air, Skydio, 2018), gasoline (military drones like MQ-9 Reaper, DRDO Rustom, Nishant, 2008), hybrid systems, solar (HALE UAVs like AeroVironment’s, 2010), or hydrogen fuel cells. Power choice depends on mission, endurance, range, and payload. Hence, option (d) is correct.

Explanation

In electric vehicle lithium-ion batteries, cobalt, lithium, and nickel form cathodes determining energy density, lifespan, cost, and performance. Graphite is used exclusively in anodes, not cathodes. Electrolytes enable lithium ion movement, while separators prevent short circuits, allowing ion flow. Lithium-ion cell types are generally recognised by the cathode material. Some of the most common lithium-ion variants (based on cell chemistry) are NMC (Lithium nickel manganese cobalt), LFP (Lithium ferro (iron) phosphate), NCA (Lithium nickel cobalt aluminium oxide), LMO (Lithium manganese oxide) and LCO (Lithium cobalt oxide). Element-Wise Analysis Cobalt: Enhances thermal stability, extends lifespan in LCO, NMC, NCA. Used in smartphones, laptops (LCO), EVs Challenges: Expensive, toxic, 70% sourced from Democratic Republic of Congo (DRC), raising ethical concerns. Lithium: Critical for cathode (LiCoO₂, LiNiMnCoO₂, LiNiCoAlO₂, LiFePO₄) and electrolyte. Enables high voltage, sourced from Lithium Triangle (Chile, Argentina, Bolivia) and Australia. Nickel: Boosts energy density, range in NMC, NCA (80% of EV battery capacity, 2021). Supplied by Indonesia, Russia, Philippines. Challenge: Reduces thermal stability, needs cobalt, manganese. Graphite: Exclusive to anodes (28% of EV battery minerals), not cathodes. Natural/synthetic graphite intercalates lithium ions for conductivity, stability. China dominates anode-grade graphite. Research explores silicon anodes. Hence, option (c) is correct.

Explanation

Ethanol and urea can be produced via coal gasification, while nitroglycerine is not practically produced due to the lack of a viable glycerol synthesis pathway from syngas. Coal Gasification: It is a thermochemical process that converts coal into syngas (synthesis gas), a mixture of carbon monoxide (CO), hydrogen (H₂), carbon dioxide (CO₂), and methane (CH₄), through partial oxidation with oxygen and steam under high temperature (1000°C or more) and pressure. Syngas serves as a versatile chemical feedstock for producing fuels, fertilizers, and chemicals, supporting India’s National Coal Gasification Mission (2021) to gasify 100 million tonnes of coal by 2030 to reduce imports of natural gas, urea, and methanol. Ethanol: Production via Coal Gasification Process: Ethanol (CHOH) is produced from syngas through catalytic conversion (e.g., Fischer-Tropsch synthesis with rhodium-based catalysts) or microbial fermentation (e.g., using Clostridium ljungdahlii). Relevance: Syngas provides carbon monoxide and hydrogen, which are converted to ethanol as part of coal-to-liquids (CTL) processes. This supports India’s 20% ethanol blending policy (G20 Biofuel Policy) to reduce crude oil imports. Nitroglycerine: Feasibility via Coal Gasification Process: Nitroglycerine (CHNO), an explosive and pharmaceutical vasodilator, is produced by nitrating glycerol with nitric acid and sulfuric acid under controlled conditions. Relevance to coal gasification:

Syngas can produce hydrogen for ammonia via the Haber-Bosch process, which is used to make nitric acid. However, glycerol synthesis from syngas (e.g., via methanol-to-olefins or propylene pathways) is commercially unviable and not documented in coal gasification applications. While syngas can indirectly support nitric acid production, the glycerol required for nitroglycerine is not practically derived from coal gasification, making the process infeasible for industrial use. Urea: Production via Coal Gasification Process: Urea (CO(NH₂)₂) is produced by reacting ammonia (NH₃) with carbon dioxide (CO₂), both derivable from syngas. Hydrogen from syngas is used in the Haber-Bosch process to produce ammonia. Carbon monoxide in syngas is converted to CO via the water-gas shift reaction (CO + H₂O → CO₂ + H₂).

Explanation

CL-20 (Chemical Formula C₆H₆N₁₂O₁₂), HMX (High Melting Explosive Chemical Formula C₄H₈N₈O₈), and LLM-105 (2,6-Diamino-3,5-dinitropyrazine-1-oxide) are High-Energy Materials (HEMs)--specifically military explosives used in warheads, missiles, artillery shells, and detonators. They are not refrigerants or fuels, but nitroamine (CL-20, HMX) or nitro-substituted (LLM-105) compounds with high detonation velocities, thermal stability, and armor-penetration capability. CL-20: Developed in 1987 by U.S. Naval Air Warfare Center, it has 20% more energy than HMX. Indian variant (ICL-20) is made by DRDO’s High Energy Materials Research Laboratory (HEMRL). Used in Switchblade drones, AGM-158C missiles, and Arjun MBT shaped charges. HMX: It is one of the Standard explosives used in Agni, Prithvi, and nuclear weapons. Used in Plastic Bonded Explosives (PBX), torpedoes, and detonators. LLM-105: Designed for Insensitive Munitions (IM), Ideal for naval/aircraft munitions, explored by HEMRL.

Explanation

Statement I is correct:The Majorana 1 chip, developed by Microsoft and announced on February 19, 2025, is the world’s first Quantum Processing Unit (QPU) using a Topological Core architecture based on topoconductors (indium arsenide and aluminum). It leverages Majorana zero modes (MZMs)--quasiparticles that are their own antiparticles--to build topological qubits. These qubits are theorized to offer inherent stability and require less error correction than traditional qubits. Microsoft claims the chip can scale up to 1 million qubits and enable fault-tolerant quantum computing for fields like drug discovery, cryptography, and materials science.

Statement II is incorrect: The Majorana 1 chip is not from AWS. AWS introduced the Ocelot chip on February 27, 2025, developed with Caltech, using cat qubits and transmons. AWS Braket, its quantum platform, supports hardware from IonQ, Rigetti, and QuEra, but has no connection to Majorana 1.

Statement III is correct: Deep learning is a specialized subfield of machine learning, which itself is a subdomain of artificial intelligence (AI). Deep learning uses artificial neural networks (ANNs) with multiple layers (e.g., convolutional neural networks (CNNs), recurrent neural networks (RNNs)) to model complex patterns in large datasets, excelling in tasks like image recognition, natural language processing, and speech recognition. Machine learning includes broader algorithms like decision trees, support vector machines (SVMs), and neural networks, with deep learning specifically requiring large datasets and computational power (e.g., GPUs).

Explanation

Statement I is correct: Monoclonal antibodies are laboratory-produced proteins created using hybridoma technology (developed in 1975) or recombinant DNA techniques, where B cells are fused with myeloma cells to produce identical antibodies targeting a specific antigen. This ensures high specificity for one antigen epitope.

Statement II is correct:

Monoclonal antibodies (mAbs) bind to specific antigens via their Fab (fragment antigen-binding) region, triggering immunological responses. The Fc (fragment crystallizable) region recruits immune cells (e.g., macrophages, NK cells) and activates the complement system, enhancing pathogen clearance and T-cell activation. While mAbs provide passive immunity and do not induce long-term immune memory, their ability to trigger ADCC, CDC, and phagocytosis constitutes immunological stimulation by engaging existing immune mechanisms.

Statement III is correct:

Therapeutic Use: Monoclonal antibodies are used to treat viral infections, including Nipah virus (NiV), a zoonotic paramyxovirus with a 40-75% fatality rate. Specific mAbs like m102.4, hu1F5, NiV41, and NiV42 target NiV G and F glycoproteins, neutralizing viral entry.

Explanation

Statement I is incorrect:

Viruses are the most abundant biological entities in marine ecosystems, with 10 million viruses per milliliter of seawater. Marine viruses, such as cyanophages and bacteriophages, infect phytoplankton, bacteria, and archaea, driving biogeochemical cycles.

Statement II is incorrect:

Bacteriophages (phages) infect only bacteria, not all microbes. Lytic phages (e.g., T4) destroy bacteria like E. coli within 20-30 minutes, while lysogenic phages (e.g., lambda) integrate into host genomes.

Statement III is incorrect:

Viruses manipulate host transcription, e.g., adenoviruses (Ad5) use E1A/E1B proteins to hijack RNA polymerase II, enhancing cyclin E and viral gene expression by 10-100 fold and suppressing IFN-. HIV uses Tat protein to boost transcription by 1000-fold; SARS-CoV-2 suppresses interferon pathways by 80%.

Explanation

The question evaluates the accuracy of botanical classifications for five plants: Cassava, Ginger, Malabar spinach, Mint, and Papaya. Key Definitions:

Woody shrub: A perennial plant with multiple woody stems branching from the base, typically under 6 m tall. Herb: A non-woody plant, often perennial or annual, with soft stems. Pseudostem: A false stem formed by tightly rolled leaf sheaths, not a true woody stem. Herbaceous climber: A non-woody plant that climbs or twines using support. Annual: Completes its life cycle in one year; perennial lives multiple years.

Pair 1 is correctly matched(Cassava - Woody Shrub):

Cassava (Manihot esculenta Crantz, Euphorbiaceae) is a tropical root crop from South America (Brazil, Paraguay). FAO and ScienceDirect classify it as a perennial woody shrub with tuberous roots (tapioca), grown as an annual. It reaches 1-3 m, with woody stems persisting in tropical climates.

Pair 2 is correctly matched(Ginger - Herb with Pseudostem):. Ginger (Zingiber officinale, Zingiberaceae) is a herbaceous perennial, grown as an annual for rhizomes. National Horticulture Board and ScienceDirect confirm its pseudostem (rolled leaf sheaths, 0.5-1.5 m) is not woody, distinguishing it from shrubs.

Pair 3 is correctly matched (Malabar Spinach - Herbaceous Climber): Malabar spinach (Basella alba/rubra, Basellaceae) is a fast-growing vine with soft, fleshy stems. ResearchGate, ICAR, and Missouri Botanical Garden classify it as a perennial herbaceous climber, twining on supports, grown as an annual in non-tropical areas.

Pair 4 is incorrectly matched (Mint - Annual Shrub): Mint (Mentha species, Lamiaceae) is a herbaceous perennial with soft, non-woody stems, spreading via runners. Indian Spices Board and Missouri Botanical Garden confirm it’s not an annual or shrub, regrowing from rhizomes yearly.

Pair 5 is incorrectly matched (Papaya - Woody Shrub): Papaya (Carica papaya, Caricaceae) is a tree-like herb or large herbaceous plant (3-10 m), with a single, hollow, fibrous stem, not woody. ICAR, ScienceDirect, and Missouri Botanical Garden classify it as a herbaceous perennial or small tree, short-lived (5-10 years), not a woody shrub.

Explanation

Statement 1 is correct: GAGAN (GPS Aided GEO Augmented Navigation) is a Satellite-Based Augmentation System (SBAS) developed jointly by the Indian Space Research Organisation (ISRO) and the Airports Authority of India (AAI). Its primary objective is to provide satellite-based navigation services with enhanced accuracy and integrity, crucial for civil aviation applications. The system improves the accuracy of GPS signals, ensuring reliable and precise navigation over the Indian airspace.

Statement 2 is correct: GAGAN facilitates more uniform and high-quality air traffic management by providing accurate navigation services across the Indian Flight Information Region (FIR). This enhancement allows for improved air traffic control, efficient flight operations, and increased safety in the aviation sector.

Statement 3 is incorrect: While GAGAN was primarily developed for aviation, its applications extend beyond this sector. The system benefits other modes of transportation and sectors such as:

Maritime Navigation: Enhancing the safety and efficiency of ship movements. Railways: Improving train tracking and management systems. Road Transport: Assisting in vehicle navigation and traffic management. Agriculture: Supporting precision farming techniques. Disaster Management: Aiding in emergency response and resource deployment.