UPSC Prelims 2025
Science & Technology Previous Year Questions (PYQs)

Detailed Explanation:

In most Lithium-ion Electric Vehicle (EV) batteries, the cathode is made using combinations of Lithium, Cobalt, and Nickel.

• Statement I (Cobalt) ✅ Correct – Used in cathodes such as NMC and LCO batteries.

• Statement II (Graphite) ❌ Incorrect – Graphite is generally used in the anode, not the cathode.

• Statement III (Lithium) ✅ Correct – A key component of all lithium-ion battery cathodes.

• Statement IV (Nickel) ✅ Correct – Commonly used in NMC and NCA cathode chemistries.

• Therefore, only three elements (Cobalt, Lithium, and Nickel) usually make up battery cathodes, making Option C the correct answer.

Element-wise Analysis

EV Battery Components

Common Cathode Chemistries

• LCO – Lithium Cobalt Oxide

• NMC – Nickel Manganese Cobalt

• NCA – Nickel Cobalt Aluminum

• LFP – Lithium Iron Phosphate

Important Facts

• Cathode materials largely determine a battery's energy density and cost.

• Graphite remains the most widely used anode material in EV batteries.

• Demand for Lithium, Nickel, and Cobalt has increased significantly due to the global EV transition.

Detailed Explanation:

CL-20, HMX, and LLM-105 are advanced high-energy explosive compounds used in military applications.

• CL-20 is one of the most powerful non-nuclear explosives developed.

• HMX is widely used in missiles, warheads, and other military munitions.

• LLM-105 is a modern explosive known for its high performance and improved thermal stability.

• Therefore, all three are explosives used in military weapons, making Option B the correct answer.

Why Other Options Are Wrong

Detailed Explanation:

Coal gasification converts coal into syngas (mainly carbon monoxide and hydrogen), which serves as a raw material for many chemicals.

• I. Ethanol ✅ Correct – Syngas can be converted into ethanol through chemical or biological processes.

• II. Nitroglycerine ❌ Incorrect – Nitroglycerine is produced by nitrating glycerol, not from syngas obtained through coal gasification.

• III. Urea ✅ Correct – Hydrogen from syngas is used to make ammonia, which then reacts with carbon dioxide to produce urea.

• Therefore, only Ethanol and Urea can be produced using coal gasification technology, making Option B the correct answer.

Substance-wise Analysis

 Coal Gasification

What is Coal Gasification?

Coal gasification is the process of converting coal into syngas, a mixture of:

• Carbon Monoxide (CO)

• Hydrogen (H₂)

• Carbon Dioxide (CO₂)

• Water Vapour

Major Products from Syngas

• Ammonia

• Urea

• Methanol

• Ethanol

• Synthetic Natural Gas (SNG)

• Hydrogen

Important Facts

• Coal gasification helps reduce dependence on imported natural gas and crude oil.

• It is an important technology for producing fertilizers and industrial chemicals.

• India is promoting coal gasification to utilize its large domestic coal reserves.

Detailed Explanation:

Monoclonal antibodies (mAbs) are laboratory-made proteins designed to recognize and bind to a specific antigen.

• Statement I is Correct: They are man-made proteins produced in laboratories.

• Statement II is Correct: They bind to specific antigens and help the immune system identify or neutralize harmful pathogens.

• Statement III is Correct: Monoclonal antibodies are used in treating and preventing certain viral infections, including the Nipah virus.

• Therefore, all three statements are correct, making Option D the correct answer.

Statement-wise Analysis

Notes: Monoclonal Antibodies (mAbs)

What are Monoclonal Antibodies?

Monoclonal antibodies are identical laboratory-produced antibodies designed to target a specific antigen.

How do they work?

• Bind to a specific antigen.

• Block pathogens from infecting cells.

• Help the immune system destroy infected or abnormal cells.

Major Uses

• Cancer treatment

• Autoimmune diseases

• Viral infections (COVID-19, Ebola, Nipah)

• Diagnostic tests

Important Facts

• Developed using a single clone of immune cells, hence the term "monoclonal."

• They are highly specific compared to conventional drugs.

• Widely used in modern biotechnology and precision medicine.

Detailed Explanation:

Alternative powertrain vehicles are vehicles that do not rely on conventional petrol or diesel internal combustion engines as their primary source of propulsion.

• Statement I is Correct: Battery Electric Vehicles (BEVs) run entirely on electricity stored in batteries.

• Statement II is Correct: Hydrogen Fuel Cell Vehicles (FCEVs) generate electricity from hydrogen using fuel cells.

• Statement III is Correct: Fuel Cell Electric Hybrid Vehicles (FCEHVs) combine fuel cells, batteries, and electric motors.

• Therefore, all three are considered alternative powertrain vehicles, making Option C the correct answer.

Vehicle-wise Analysis

Alternative Powertrain Vehicles

What are Alternative Powertrains?

These are vehicle propulsion systems that use alternatives to conventional petrol or diesel engines.

Major Types

Important Facts

• BEVs produce zero tailpipe emissions.

• FCEVs emit only water vapor as a by-product.

• Hydrogen-based vehicles are considered important for long-range and heavy-duty transport.

• Alternative powertrains help reduce dependence on fossil fuels and lower carbon emissions.

Detailed Explanation:

The capabilities of Unmanned Aerial Vehicles (UAVs) depend on their design (fixed-wing, multirotor, hybrid, etc.). Therefore, the word "All" makes all three statements incorrect.

• Statement I is Incorrect: Not all UAVs can perform vertical landing. Fixed-wing UAVs require a runway or launcher/recovery system.

• Statement II is Incorrect: Not all UAVs can hover. Fixed-wing UAVs must keep moving forward to stay airborne.

• Statement III is Incorrect: Not all UAVs use battery power only. Many UAVs use fuel engines, hybrid systems, or even solar power.

• Therefore, none of the statements are correct, making Option D the correct answer.

Statement-wise Analysis

Types of UAVs

Important Facts

• Fixed-wing UAVs are preferred for long-range surveillance and mapping.

• Multirotor drones are ideal for photography, monitoring, and inspection.

• Hybrid UAVs combine the advantages of fixed-wing and multirotor systems.

• Modern UAVs can be powered by batteries, internal combustion engines, hydrogen fuel cells, or solar energy.

Detailed Explanation:

Detailed Explanation:

All three statements are incorrect because viruses are found in diverse environments, can infect bacteria, and can manipulate host cell functions.

• Statement I is Incorrect: Viruses are extremely abundant in oceans and play an important role in marine ecosystems.

• Statement II is Incorrect: Certain viruses called bacteriophages specifically infect bacteria.

• Statement III is Incorrect: Viruses can alter the host cell's transcriptional machinery to produce viral proteins and replicate themselves.

• Therefore, none of the statements are correct, making Option D the correct answer.

Statement-wise Analysis

Viruses

What are Viruses?

Viruses are microscopic infectious agents that can reproduce only inside living host cells.

Important Facts

• Found in soil, air, freshwater, oceans, and living organisms.

• Cannot reproduce independently.

• Use host cell machinery to make new viruses.

• Can infect animals, plants, fungi, and bacteria.

Bacteriophages

• Viruses that infect bacteria.

• Among the most abundant biological entities on Earth.

• Widely used in biotechnology and phage therapy research.

How Viruses Affect Host Cells

Viruses can:

• Alter gene expression.

• Hijack cellular machinery.

• Suppress immune responses.

• Change transcription and protein synthesis pathways.

Detailed Explanation:

Among the three pairs, Dornier-228 and C-17 Globemaster III are correctly matched with their roles, while IL-76 is incorrectly described.

• Pair I is Correct: Dornier-228 is used for maritime patrol, surveillance, and reconnaissance missions.

• Pair II is Incorrect: IL-76 is a heavy military transport aircraft, not a supersonic combat aircraft.

• Pair III is Correct: C-17 Globemaster III is a strategic military transport aircraft used for troop and cargo movement.

• Therefore, only two pairs are correctly matched, making Option B the correct answer.

Pair-wise Analysis

Important Transport Aircraft of India

Dornier-228

• Twin-engine utility aircraft.

• Used for maritime patrol, surveillance, search and rescue.

• Operated by the Indian Navy and Coast Guard.

IL-76

• Heavy strategic transport aircraft of Russian origin.

• Used for troop transport, cargo movement, and humanitarian missions.

• Also serves as a platform for AWACS variants.

C-17 Globemaster III

• Strategic military transport aircraft manufactured by Boeing.

• Can carry troops, tanks, helicopters, and heavy equipment.

• Backbone of India's long-range airlift capability.

Detailed Explanation:

Rare Earth Elements (REEs) such as Europium, Terbium, and Yttrium are widely used in modern display technologies.

• Statement I is Correct: Some rare earth elements are used in flat TV screens and computer monitors.

• Statement II is Correct: These elements possess phosphorescent properties, meaning they can absorb energy and emit light.

• Statement II explains Statement I because these phosphorescent properties help produce bright, vibrant, and accurate colors in display screens.

• Therefore, Option A is the correct answer.

Statement-wise Analysis

Rare Earth Elements (REEs)

What are Rare Earth Elements?

Rare Earth Elements are a group of 17 metallic elements consisting of:

• 15 Lanthanides

• Scandium

• Yttrium

Important Applications

• Flat-screen TVs and monitors

• Smartphones

• Electric Vehicles (EVs)

• Wind turbines

• Defence equipment

• Medical imaging devices

Phosphorescence

Phosphorescence is the ability of a material to:

• Absorb energy

• Store it temporarily

• Emit light gradually

This property helps create:

• Bright displays

• High color accuracy

• Better screen efficiency

Important REEs Used in Displays

Detailed Explanation:

GAGAN (GPS-Aided Geo Augmented Navigation) is India's Satellite-Based Augmentation System (SBAS), jointly developed by ISRO and the Airports Authority of India (AAI) to improve GPS-based navigation.

• Statement I is Correct: GAGAN enhances the accuracy and integrity of GPS signals.

• Statement II is Correct: It enables safer, more efficient, and uniform air traffic management.

• Statement III is Incorrect: GAGAN is useful not only in aviation but also in road transport, railways, maritime navigation, agriculture, surveying, and disaster management.

• Therefore, only Statements I and II are correct, making Option D the correct answer.

Statement-wise Analysis

Detailed Explanation:

The question asks for the statements that are not correct.

• Statement I is Incorrect: The National Rail Plan (NRP) aims to create a future-ready railway system by 2030, not 2028.

• Statement II is Incorrect: Kavach is an indigenous Automatic Train Protection (ATP) system developed under the Make in India initiative, not in collaboration with Germany.

• Statement III is Correct: Kavach uses RFID tags fitted on tracks and station sections to continuously monitor train location and movement.

• Therefore, Statements I and II are not correct, making Option A the correct answer.

Statement-wise Analysis

Kavach System

What is Kavach?

• Kavach is India's indigenous Automatic Train Protection (ATP) system.

• Developed under the Make in India initiative by Indian Railways.

• Designed to prevent train collisions and improve railway safety.

Key Features

• Automatic braking if the driver fails to respond.

• Prevents Signal Passed At Danger (SPAD).

• Real-time train location monitoring.

• Uses RFID tags, radio communication, and onboard equipment.

National Rail Plan (NRP)

• Released by Indian Railways.

• Vision to create a future-ready railway network by 2030.

• Focuses on capacity enhancement, freight share increase, and modernization.

Detailed Explanation:

Among the given missions, Axiom-4 and Gaganyaan directly support and promote micro-gravity research, whereas SpaDeX is mainly a technology demonstration mission.

• Statement I is Correct: Axiom-4 carries scientific experiments and micro-gravity research payloads aboard the International Space Station (ISS).

• Statement II is Incorrect: SpaDeX (Space Docking Experiment) is designed to demonstrate autonomous docking technology, not primarily for micro-gravity research.

• Statement III is Correct: Gaganyaan includes several micro-gravity experiments to be conducted by Indian astronauts (Vyomanauts) in space.

• Therefore, only two missions support micro-gravity research, making Option B the correct answer.

Mission-wise Analysis

Micro-gravity Research

What is Micro-gravity?

Micro-gravity is a condition in space where objects experience very weak gravity and appear to be weightless.

Why is it Important?

Micro-gravity helps scientists study:

• Human health in space

• Material science

• Biotechnology

• Fluid dynamics

• Plant growth and agriculture

Detailed Explanation:

Correct Answer: ✅ Option 3 (I, II and III)

Direct Air Capture (DAC) is an emerging technology that removes carbon dioxide (CO₂) directly from the atmosphere. The captured CO₂ can either be permanently stored underground (carbon sequestration) or utilized in various industrial applications, making it an important tool in climate change mitigation.

✅ Statement I is Correct: DAC can capture atmospheric CO₂ and store it permanently underground, helping in carbon sequestration.

✅ Statement II is Correct: Captured CO₂ can be used in the production of plastics, chemicals, beverages, and food processing industries.

✅ Statement III is Correct: In aviation, captured CO₂ can be combined with green hydrogen to produce synthetic low-carbon aviation fuels (e-fuels).

Short Notes: Direct Air Capture (DAC)

• DAC removes CO₂ directly from ambient air.

• It is considered a Negative Emission Technology (NET).

• Captured CO₂ can be stored underground or utilized industrially.

• DAC supports carbon sequestration and climate mitigation efforts.

• CO₂ from DAC can be used to manufacture plastics, chemicals, and synthetic fuels.

• Synthetic aviation fuels are produced by combining captured CO₂ with green hydrogen.

• Major challenges include high energy requirements and operational costs.