Solved UPSC Prelims S&T PYQs With Explanation 2025 

1. 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

1. Ans-c

Explanation

 Approaches  to decarbonise the transport sector and reduce the use of fossil fuels:

1. Alternative powertrains—These are powertrains that are not based exclusively on the internal combustion engine. The main options include hybrids and plug-in hybrids, full battery electrics, and hydrogen fuel cell vehicles , Fuel cell electric vehicles (FCEVs)
2. Low carbon fuels—These are liquid or gaseous fuels that can be used in combustion engines, existing or modified. The main options include e-fuels (i.e., synthetic fuels produced using electrical energy) and biofuels.

Hence all the three are correct

2. 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 battery 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

2. Ans-d

Explanation

Early UAVs development is generally divided into two separate types, Fixed Wing UAV (FWUAV), and rotorcraft UAV (RUAV). 

FWUAVs typically have longer endurance and thus can reach further than RUAV in a single flight, but require runways for take-offs and landings. 

RUAVs on the other hand, are more manoeuvrable and able to take-off and land vertically without any runway but has much lesser endurance due to their low efficiency in power consumption and low speed.

Hybrid Vertical-Take-Off-Landing (VTOL) aircraft will have the advantages of both FWUAV and RUAV 

Drones, are generally classified as single rotor (helicopter), multi-rotor (multicopter), fixed wing, and fixed-wing hybrid VTOL according to their physical structures.

Single-rotor drones are small-sized helicopters, and fueled or electric types are available. Working with a single blade and fuel offers advantages such as increasing stability and flying longer distances, but it also brings safety risks.

Multicopters are the smallest, lightest, and most widely used drones on the market. Multicopters are divided into models with four engines (quadcopter), six engines (hexacopter), and eight engines (octocopter) according to the number of motors.

Fixed-wing drones: Unlike rotary wings, they use wings like a regular airplane instead of vertical lift rotors to provide lift . In other words, they only need to use energy to move forward. They are much more efficient as they do not use additional power to stay in the air, so they can cover longer distances and scan much larger areas. Gasoline-powered ones can remain in the air for 16 hours or more.

The main disadvantage of a fixed-wing aircraft is that they cannot fly in one spot. Depending on their size, they need a runway or launcher to get them into the air. Fixed-wing also makes launching and landing them much more difficult, as a runway, parachute, or net may be needed for a safe landing again after the flight.

Fixed-wing hybrid Vertical-Take-Off-Landing(VTOL)drone: Fixed-wing hybrid VTOL drones are a new hybrid category that can also take off and land vertically, combining the advantages of fixed-wing UAVs and the ability to hover. 

Fixed-wing hybrid VTOL unmanned aerial vehicles have the advantages of flying vertically and hovering, offering greater versatility than fixed-wing drones and the durability needed to travel long distances with heavy payloads. On the other hand, they could be better in both forward flying and hovering features and the need for specialised personnel in the flight and control of these types of drones is an important consideration.

Their power sources classify drones as battery-powered, gasoline-powered, hydrogen fuel cell, and solar drones. 

Hence none of the statements are correct 

3. 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

3. Ans-c

Explanation

Every electric vehicle (EV) is a lithium-ion battery that depends on several key minerals that help power it. The minerals used are

Hence, only 1, 2, 4 are correct 

4. Consider the following: 

I. Cigarette butts 

II. Eyeglass lenses 

III. Car tyres 

How many of them contain plastic? 

(a) Only one 

(b) Only two 

(c) All the three 

(d) None

4. Ans-c

Explanation

Cigarette butts are actually the most abundant form of plastic waste in the world.

Common Eyeglass Lens Materials- Standard glass ,Standard plastic ,Polycarbonate, Trivex.

Car tyres are made from around 24 per cent synthetic rubber – a variation of plastic made using petroleum by-products – that breaks down as the vehicles travel.

Microplastic residue from car tyres account for 28% of microplastics entering the environment globally.

All the three are correct .

5. Consider the following substances: 

I. Ethanol 

II. Nitroglycerine 

III. Urea 

Coal gasification technology can be used in the production of how many of them? 

(a) Only one 

(b) Only two 

(c) All the three 

(d) None

5. Ans-b

Explanation

Coal is one of the most abundant natural resources in the country. Coal gasification technology enables conversion of coal into syngas (synthetic gas)

Syngas can be used to produce Gaseous Fuels such as Hydrogen, Substitute Natural Gas (SNG or Methane), Di-Methyl Ether (DME), Liquid Fuels such as Methanol, Ethanol, Synthetic diesel and Chemical and Petrochemicals like Methanol derivatives, Olefins, Propylene, Mono-Ethylene Glycol (MEG). Acetic Acid ,  Formaldehyde , nitrogenous fertilizers including Ammonia , Urea, Ammonium nitrate , DAP  

Hence 1 and 3 are correct 

Nitroglycerine is an explosive liquid which was first made by Ascanio Sobrero in 1846 by treating glycerol with a mixture of nitric and sulphuric acid. It is not produced by Coal Gasification . 

Hence2 is in correct 

6. What is the common characteristic of the chemical substances generally known as CL-20, HMX and LLM-105, which are sometimes talked about in 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

6. Ans-b

Explanation

CL-20, or Octa-Nitro-Cubane, is a Nitramine class of explosive 15 times as powerful as HMX, His/Her Majesty Explosive or High Melting Explosive or Octogen.

CL-20, so named after the China Lake facility of the Naval Air Weapons Station in California, US, was first synthesized by Dr. Arnold Nielson in 1987. HMX dates from 1941

LLM-105 was first produced at Lawrence Livermore National Laboratory in 1995.  It can withstand high temperatures without blowing up, making it a candidate for warheads used in hypersonic missiles, which fly and manoeuvre at more than five times the speed of sound. 

7. Consider the following statements:

I. It is expected that 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

7. Ans-c

Explanation

Microsoft has recently unveiled a groundbreaking advancement in quantum computing with the introduction of its new quantum chip, Majorana 1.

Hence Statement 1 is correct

Amazons first-ever quantum computing chip is  Ocelot.

Hence Statement 2 is incorrect

Deep learning is a subset of machine learning that uses multilayered neural networks, called deep neural networks, to simulate the complex decision-making power of the human brain. Some form of deep learning powers most of the artificial intelligence (AI) applications in our lives today 

Hence Statement 3 is correct

8. 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

8. Ans-d

Explanation

‘Mono’ means ‘one’ and ‘clone’ means ‘identical copy’. Monoclonal antibodies are identical copies of one type of antibody.

The production of monoclonal antibodies is an in vitro process by the use of tissue-culture techniques.

Hence statement 1 is correct 

Antibodies are proteins produced by a type of white blood cell called a lymphocyte. Pathogens have proteins on their surface called antigens. When a pathogen infects the body, the lymphocytes recognise these antigens as foreign and attack them by producing antibodies.

Antibodies bind to specific antigens on pathogens. This means that only one type of antibody will bind to a matching antigen.

Hence statement 2 is correct 

Monoclonal antibodies, as a highly effective immunotherapeutic treatment against viral infections, are now widely used for pre- or postexposure protection against infectious diseases caused by highly virulent and lethal viruses, such as Ebola virus (EBOV)and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and Nipah virus (NiV)

NiV41 and NiV42 – Two neutralising antibodies (NiV41 and NiV42) targeting the NiV receptor binding protein (RBP) were identified. antibodies derived from NiV41 display cross-reactivity against both NiV and Hendra virus (HeV), whereas the antibody based on NiV42 is only specific to NiV. 

Hence statement 3 is correct 

9. 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

9. Ans-d

Explanation

Viruses inhabit the world’s oceans in great numbers. One spoonful of seawater can hold up to a billion virus particles

Hence statement 1 is incorrect 

A bacteriophage is a type of virus that infects bacteria. The word “bacteriophage” literally means “bacteria eater,” because bacteriophages destroy their host cells. 

Hence statement 2 is incorrect 

The ability to shut off host gene expression is a shared feature of many viral infections, and it is thought to promote viral replication by freeing host cell machinery and blocking immune responses. 

Hence statement 3 is incorrect 

10. Consider the following statements: 

Statement I: Activated carbon is a good and an attractive tool to remove pollutants from effluent streams and to remediate contaminants from various industries. 

Statement II:Activated carbon exhibits a large surface area and a strong potential for adsorbing heavy metals. 

Statement III: Activated carbon can be easily synthesized from environmental wastes with high carbon content. 

Which one of the following is correct in respect of the above statements? 

(a) Both statement II and Statement III are correct and both of them explain Statement I 

(b) Both Statement II and Statement III are correct but only one of them explains Statement I 

(c) Only one of the Statements II and III is correct and that explains Statement I 

(d) Neither Statement II nor Statement III is correct.

10. Ans-c

Explanation

Activated carbons are produced from carbon of vegetable origin (peat, lignite, coal or nutshells). The activation process creates an extensive pore structure that allows considerable adsorption onto an active surface area above 400 m2/g.

Activated carbon products can be put to a range of uses, including the purification, concentration and separation of gases from liquids, purifying drinking water, waste water and sewage treatment as well as controlling emissions. They also have further applications in the food, chemical and pharmaceutical industries.

Hence statement 2 is correct 

The production method  of  activated carbon consists of the following main process steps:

Devolatilization and Carbonization of raw material

The Carbonization process comprises heating of the raw material to a temperature around 600 °C. This process also removes volatiles from the raw material

Activation of the carbonized material

The carbonized material is activated at temperatures around 950 °C with a gasification agent (usually steam) which removes a proportion of the carbon atoms by gasification 

The steam activation process steps are performed in reactors such as rotary kilns, multiple hearth kilns, shaft kilns, and other high temperature kilns. 

So It cannot be easily synthesised , it involves substantial costs .

Hence statement 3 is incorrect 

So Only Statements II is correct and that explains Statement I 

11. GPS-Aided Geo Augmented Navigation (GAGAN) uses a system of ground stations to provide necessary augmentation. Which of the following statements is/are correct in respect of GAGAN?

I. It is designed to provide additional accuracy and integrity.

II. It will allow more uniform and high quality air traffic management.

III. It will provide benefits only in aviation but not in other modes of transportation.

Select the correct answer using the code given below.

(a) I, II and III

(b) II and III only

(c) I only

(d) I and II only

11. Ans-d

Explanation

GAGAN is the acronym for GPS Aided GEO Augmented Navigation. The GAGAN uses a system of ground stations to provide necessary augmentations to the GPS standard positioning service(SPS) navigation signal. A network of precisely surveyed ground reference stations (INdianReference Stations  INRES) is strategically positioned across the country to collect GPS satellite data. Using this information, the master control centre (INdian Master Control Centre  INMCC) generates messages to correct any signal errors. These correction messages are then uplinked through (INdian Land Uplink Station INLUS) and broadcast through communication satellites (Geostationary) to receivers onboard aircraft using the same frequency as GPS. 

The GAGAN is designed to provide the additional accuracy, availability, and integrity necessary to enable users to rely on GPS for all phases of flight, from en route through approach for all qualified airports within the GAGAN service volume. 

Hence statement 1 is correct

GAGAN will also provide the capability for increased accuracy in position reporting, allowing for more uniform and high-quality Air Traffic Management (ATM).

Hence statement 2 is correct

In addition, GAGAN will provide benefits beyond aviation to all modes of transportation, including maritime, highways, and railroads 

Hence statement 3 is incorrect

12. Consider the following statements:

Statement I: Some rare earth elements are used in the manufacture of flat television, screens and computer monitors,

Statement II:Some rare earth elements have phosphorescent properties.

Which one of the following is correct in respect of the above statements?

(a) Both Statement I and Statement II are correct and Statement II explains Statement I

(b) Both Statement I and Statement II are correct but Statement II doesnot explain Statement I

(c) Statement I is correct but Statement II is not correct

(d) Statement I is not correct but Statement II is correct

12. Ans-a

Explanation

Rare earth elements are used in several high technology industrial products.

In the ceramic and glass industry rare earth element containing compounds are used for high temperature materials, for coatings, polishing, coloring, decoloring and as glass additives. The main other uses of rare earth elements are in permanent magnets, phosphors in color television tubes, x-ray tubes, fluorescent lamps, electronic and computer devices and lighter flints. 

Hence statement 1 is correct 

Rare Earth Metals (REM) like europium and terbium are known for their phosphorescent properties

Hence statement 2 is correct  and explains statement 1

13. Consider the following statements:

I. Indian Railways have prepared a National Rail Plan (NRP) to create a future ready railway system by 2028.

II. ‘Kavach’ an Automatic Train Protection system developed in collaboration with Germany.

III. ‘Kavach’ system consists of RFID tags fitted on track in station section.

Which of the statements given above are not correct?

(a) I and II only

(b) II and III only

(c) I and III only

(d) 1, II and III

13. Ans- a

Explanation

Indian Railways have prepared a National Rail Plan (NRP) for India – 2030. The Plan is to create a ‘future ready’ Railway system by 2030. 

Statement 1 is incorrect

Kavach is an indigenously developed Automatic Train Protection (ATP) system.

Statement 2 is incorrect

India’s capability to deploy the Kavach automatic train collision avoidance system is set to receive a boost with the approval of global companies, Germany’s Siemens and Japan’s Kyosan, to install it on the national transporter

Kavach aids the Loco Pilot in running of train within specified speed limits by automatic application of brakes in case Loco Pilot fails to do so and also helps the trains to run safely during inclement weather

Kavach was adopted as National ATP system in July 2020.

Implementation of Kavach System involves following Key Activities:

1. Installation of Station Kavach at each and every station, block section.
2. Installation of RFID Tags throughout the track length.
3. Installation of telecom Towers throughout the section.
4. Laying of Optical Fibre Cable along the track.
5. Provision of Loco Kavach on each and every Locomotive running on Indian Railways.

Statement 3 is correct

14. Consider the following Space missions :

I. Axiom-4

II. SpaDeX

III. Gaganyaan

How many of the space missions given above encourage and support micro-gravity research?

(a) Only one

(b) Only two

(c) All the three

(d) None

14. Ans-c

Explanation

The Axiom-4 mission

The Axiom-4 mission  a collaborative effort of Axiom Space, NASA, European Space Agency (ESA) and Indian Space Research Organisation (ISRO)

During the 14-day mission docked to the orbiting laboratory, the astronauts will conduct global outreach activities, microgravity research and technology demonstrations.

PSLV-C60 SpaDeX mission

SpaDeX mission is a cost-effective technology demonstrator mission for the demonstration of in-space docking using two small spacecraft launched by PSLV.

PS4-Orbital Experiment Module, designated as POEM, refers to the usage of the spent fourth stage of the Polar Synchronous Launch Vehicle (PSLV). It provides an opportunity for the scientific community to carry out certain in-orbit microgravity experiments for an extended duration of up to three months

PSLV-C60 SpaDeX mission is the fourth POEM Mission (in short POEM-4) in the series. 

Gaganyaan 

Indian Human Space Program, Gaganyaan aims to encourage and support Indian scientific community in microgravity research activities through flight opportunities in ISRO’s missions as well as joint international efforts.

15. With reference to India’s defence, consider the following pairs:

Aircraft type                     : Description

I. Dornier-228                   : Maritime patrol aircraft

II. IL-76                               : Supersonic combat aircraft

III. C-17 Globe-master III  : Military transport aircraft

How many of the pairs given above are correctly matched?

(a) Only one

(b) Only two

(c) All the three

(d) None

15. Ans-b

Explanation

Dornier-228

The Dornier 228 is a high-wing, twin-engine turboprop aircraft manufactured by Hindustan Aeronautics Limited (HAL) and RUAG Aerospace. The DO-228 is capable of carrying payloads up to around 5,200 lbs and has a maximum flight altitude of around 28,000 ft. It has been utilized for remote sensing and atmospheric research.

The Do-228 can be deployed in passenger and cargo transportation, as an air taxi, for corporate purposes, for aircrew training, maritime surveillance, search and rescue, border patrolling and medical evacuation missions.

Hence 1st pair is correctly matched

 IL-76

The Ilyushin Il-76 is a robust cargo aircraft celebrated for its significant payload capacity and ability to transport bulk, heavy, and outsized loads. Its solid construction and advanced engineering make it ideal for a wide range of logistical and transport operations. 

The Ilyushin Il-76, developed by the Ilyushin Design Bureau, first flew in 1971. It was originally designed to meet the airlift needs of the Soviet Union, capable of transporting heavy machinery, military equipment, and large cargo. 

Hence 2nd  pair is incorrectly matched

C-17 Globe-master III

A high-wing, four-engine, T-tailed military transport aircraft, the multi-service C-17 can carry large equipment, supplies and troops directly to small airfields in harsh terrain anywhere in the world. The massive, sturdy, long-haul aircraft tackles distance, destination and heavy, oversized payloads in unpredictable conditions. It has delivered cargo in every worldwide operation since the 1990s.

Boeing has partnered with the U.S. Air Force on C-17 sustainment since the delivery of the first aircraft in 1993. 

Hence 3rd pair is correctly matched

16. Artificial way of causing rainfall to reduce air pollution makes use of

(a) silver iodide and potassium iodide

(b) silver nitrate and potassium iodide

(c) silver iodide and potassium nitrate

(d) silver nitrate and potassium chloride

16. Ans-a

Explanation

Cloud seeding is a weather modification technique that improves a cloud’s ability to produce rain, in order to tackle pollution.

The most common chemicals used for cloud seeding include silver iodide, potassium iodide and dry ice (solid carbon dioxide)