Science — UPSC Prelims PYQs

Question 1

Consider the following substances:
1. Ethanol
2. Nitroglycerine
3. Urea
Coal gasification technology can be used in the production of how many of them? (A) Only one (B) Only two (C) All three (D) None

Accepted Answer

(C) All three — Correct. Coal gasification yields synthesis gas, which can be catalytically converted to ethanol, used to produce ammonia for urea, and processed into nitroglycerine precursors.

Question 2

With reference to Unmanned Aerial Vehicles (UAVs), consider the following statements:
1. All types of UAVs can do vertical landing.
2. All types of UAVs can do automated hovering.
3. 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 three (D) None

Accepted Answer

(D) None — Correct. Fixed-wing UAVs cannot do vertical landing or automated hovering, and many UAVs use internal combustion engines or hybrid power, not batteries alone.

Question 3

Consider the following statements:
1. No virus can survive in ocean waters.
2. No virus can infect bacteria.
3. No virus can change the cellular transcriptional activity in host cells.
Which of the statements given above are correct? (A) Only one (B) Only two (C) All three (D) None

Accepted Answer

(D) None — Correct. Marine viruses (bacteriophages) thrive in oceans; bacteriophages specifically infect bacteria; and many viruses alter host cell transcription by hijacking cellular machinery.

Question 4

Consider the following space missions:
1. Axiom-4
2. SpaDeX
3. Gaganyaan
How many of the space missions given above encourage and support micro-gravity research? (A) Only one (B) Only two (C) All three (D) None

Accepted Answer

(C) All three — Correct. Axiom-4 conducts micro-gravity experiments on the ISS, SpaDeX demonstrates docking for future space station modules, and Gaganyaan is India's crewed mission with micro-gravity research payloads.

Question 5

Consider the following statements:
1. It is expected that Majorana 1 chip will enable quantum computing.
2. Majorana 1 chip has been introduced by Amazon Web Services (AWS).
3. Deep learning is a subset of machine learning.
Which of the statements given above are correct? (A) 1 and 2 only (B) 2 and 3 only (C) 1 and 3 only (D) 1, 2 and 3

Accepted Answer

(C) 1 and 3 only — Correct. The Majorana 1 chip, developed by Microsoft, is designed to advance quantum computing using topological qubits. Deep learning is indeed a subset of machine learning that uses multi-layered neural networks.

Question 6

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 does not 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

Accepted Answer

(A) Both Statement-I and Statement-II are correct and Statement-II explains Statement-I — Correct. Rare earth elements like europium and terbium are used in display phosphors. Their phosphorescent properties are the reason they are employed in screens and monitors.

Question 7

In the context of electric vehicle batteries, consider the following elements:
1. Cobalt
2. Graphite
3. Lithium
4. Nickel
How many of the above usually make up battery cathodes? (A) Only one (B) Only two (C) Only three (D) All the four

Accepted Answer

(C) Only three — Correct. Cobalt, lithium and nickel are standard cathode components in Li-ion batteries. Graphite is used as the anode material, not the cathode.

Question 8

Consider the following statements:
1. Indian Railways have prepared a National Rail Plan (NRP) to create a future ready railway system by 2028.
2. 'Kavach' is an Automatic Train Protection system developed in collaboration with Germany.
3. 'Kavach' system consists of RFID tags fitted on track in station section.
Which of the statements given above are not correct? (A) 1 and 2 only (B) 2 and 3 only (C) 1 and 3 only (D) 1, 2 and 3

Accepted Answer

(A) 1 and 2 only — Correct. The NRP target year is 2030, not 2028, and Kavach was developed indigenously by RDSO (Research Designs and Standards Organisation), not with Germany.

Question 9

Consider the following statements:
Statement-I: Giant stars live much longer than dwarf stars.
Statement-II: Compared to dwarf stars, giant stars have a greater rate of nuclear reactions.
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 does not explain Statement-I (C) Statement-I is correct, but Statement-II is incorrect (D) Statement-I is incorrect, but Statement-II is correct

Accepted Answer

(D) Statement-I is incorrect, but Statement-II is correct — Correct. Giant stars have higher nuclear reaction rates (Statement-II is true) but this causes them to exhaust fuel faster, giving them shorter, not longer, lifespans (Statement-I is false).

Question 10

Which one of the following words/phrases is most appropriately used to denote "an interoperable network of 3D virtual worlds that can be accessed simultaneously by millions of users, who can exert property rights over virtual items"? (A) Big data analytics (B) Cryptography (C) Metaverse (D) Virtual matrix

Accepted Answer

(C) Metaverse — Correct. The Metaverse describes an interoperable network of persistent 3D virtual worlds where users can interact, own virtual property, and conduct transactions.

Question 11

Which one of the following is synthesised in human body that dilates blood vessels and increases blood flow? (A) Nitric oxide (B) Nitrous oxide (C) Nitrogen dioxide (D) Nitrogen pentoxide

Accepted Answer

(A) Nitric oxide — Correct. Nitric oxide (NO) is produced by endothelial cells lining blood vessels and acts as a vasodilator, relaxing smooth muscle and increasing blood flow.

Question 12

Consider the following activities:
1. Identification of narcotics on passengers at airports or in aircraft
2. Monitoring of precipitation
3. Tracking the migration of animals
In how many of the above activities can radars be used? (A) Only one (B) Only two (C) All three (D) None

Accepted Answer

(C) All three — Correct. Millimetre-wave scanners (a radar type) detect concealed substances at airports, weather radars monitor precipitation, and Doppler radars track animal migration patterns.

Question 13

In which of the following are hydrogels used?
1. Controlled drug delivery in patients
2. Mobile air-conditioning systems
3. Preparation of industrial lubricants
Select the correct answer using the code given below: (A) 1 only (B) 1 and 2 only (C) 2 and 3 only (D) 1, 2 and 3

Accepted Answer

(D) 1, 2 and 3 — Correct. Hydrogels are used in drug delivery (controlled release matrices), air-conditioning systems (desiccant cooling), and as bases for industrial lubricants.

Question 14

With reference to radioisotope thermoelectric generators (RTGs), consider the following statements:
1. RTGs are miniature fission reactors.
2. RTGs are used for powering the onboard systems of spacecrafts.
3. RTGs can use Plutonium-238, which is a by-product of weapons development.
Which of the statements given above are correct? (A) 1 and 2 only (B) 2 and 3 only (C) 1 and 3 only (D) 1, 2 and 3

Accepted Answer

(B) 2 and 3 only — Correct. RTGs rely on radioactive decay (not fission) to generate electricity for spacecraft, and they commonly use Plutonium-238 originally produced in weapons-grade reactor programmes.

Question 15

Consider the following pairs:
Objects in space : Description
1. Cepheids — Giant clouds of dust and gas in space
2. Nebulae — Stars which brighten and dim periodically
3. Pulsars — Neutron stars that are formed when massive stars run out of fuel and collapse
How many of the above pairs are correctly matched? (A) Only one (B) Only two (C) All three (D) None

Accepted Answer

(A) Only one — Correct. Only pair 3 is correct. Cepheids are variable stars (not dust clouds), nebulae are gas-dust clouds (not variable stars), and pulsars are indeed rapidly rotating neutron stars formed from collapsed massive stars.

Question 16

'Aerial metagenomics' best refers to which one of the following situations? (A) Collecting DNA samples from air in a habitat at one go (B) Understanding the genetic makeup of avian species of a habitat (C) Using air-borne devices to collect blood samples from moving animals (D) Sending drones to inaccessible areas to collect plant and animal samples from land surfaces and water bodies

Accepted Answer

(A) Collecting DNA samples from air in a habitat at one go — Correct. Aerial metagenomics involves sampling environmental DNA (eDNA) directly from air to catalogue biodiversity in a habitat without capturing organisms.

Question 17

Consider the following statements:
1. Carbon fibres are used in the manufacture of components used in automobiles and aircraft.
2. Carbon fibres once used cannot be recycled.
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

Accepted Answer

(A) 1 only — Correct. Carbon fibres are widely used in automobile and aircraft components for their high strength-to-weight ratio. However, carbon fibre recycling technologies (pyrolysis, solvolysis) do exist, making statement 2 incorrect.

Question 18

Which one of the following countries has its own Satellite Navigation System? (A) Australia (B) Canada (C) Israel (D) Japan

Accepted Answer

(D) Japan — Correct. Japan operates the Quasi-Zenith Satellite System (QZSS), a regional satellite navigation system that augments GPS coverage over Japan and the Asia-Oceania region.

Question 19

'Microsatellite DNA' is used in the case of which one of the following? (A) Studying the evolutionary relationships among various species of fauna (B) Stimulating stem cells to transform into diverse functional tissues (C) Promoting clonal propagation of horticulture plants (D) Assessing the efficacy of drugs by conducting series of drug trials in a population

Accepted Answer

(A) Studying the evolutionary relationships among various species of fauna — Correct. Microsatellite DNA (short tandem repeats) varies between individuals and species, making it a standard molecular marker for phylogenetic and population genetics studies.

Question 20

Consider the following statements:
Statement-I: India, despite having uranium deposits, depends on coal for most of its electricity production.
Statement-II: Uranium, enriched to the extent of at least 60%, is required for the production of electricity.
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 is the correct explanation for Statement-I (B) Both Statement-I and Statement-II are correct and Statement-II is not the correct explanation for Statement-I (C) Statement-I is correct but Statement-II is not correct (D) Statement-I is not correct but Statement-II is correct

Accepted Answer

(C) Statement-I is correct but Statement-II is not correct — Correct. India does rely on coal for the bulk of its electricity despite having uranium reserves. However, nuclear power reactors use low-enriched uranium (about 3-5% U-235), not 60%.

Question 21

'Wolbachia method' is sometimes talked about with reference to which one of the following? (A) Controlling the viral diseases spread by mosquitoes (B) Converting crop residues into packing material (C) Producing biodegradable plastics (D) Producing biochar from thermo-chemical conversion of biomass

Accepted Answer

(A) Controlling the viral diseases spread by mosquitoes — Correct. Wolbachia are intracellular bacteria introduced into Aedes aegypti mosquitoes to reduce their ability to transmit dengue, Zika, and chikungunya viruses.

Question 22

Some microorganisms can grow in environments with temperature above the boiling point of water. Some can grow below the freezing point of water. Some can grow in highly acidic environments with a pH below 3.
How many of the above statements are correct? (A) Only one (B) Only two (C) All three (D) None

Accepted Answer

(C) All three — Correct. Thermophiles thrive above 100 °C near hydrothermal vents, psychrophiles grow below 0 °C in polar ice, and acidophiles flourish at pH below 3 in acid mine drainage.

Question 23

Consider the following statements:
DNA Barcoding can be a tool to:
1. Assess the age of a plant or animal.
2. Distinguish among species that look alike.
3. Identify undesirable animal or plant materials in processed foods.
Which of the statements given above is/are correct? (A) 1 only (B) 3 only (C) 1 and 2 (D) 2 and 3

Accepted Answer

(D) 2 and 3 — Correct. DNA barcoding uses short standardised gene regions to distinguish morphologically similar species and to detect adulteration in processed foods.

Question 24

Consider the following statements:
1. Biofilms can form on medical implants within human tissues.
2. Biofilms can form on food and food processing surfaces.
3. Biofilms can exhibit antibiotic resistance.
Which of the statements given above are correct? (A) 1 and 2 only (B) 2 and 3 only (C) 1 and 3 only (D) 1, 2 and 3

Accepted Answer

(D) 1, 2 and 3 — Correct. Biofilms form on implants, food surfaces, and exhibit antibiotic resistance due to their protective extracellular polymeric substance matrix.

Question 25

With reference to "Software as a Service (SaaS)", consider the following statements:
1. SaaS buyers can customise the user interface and can change data fields.
2. SaaS users can access their data through their mobile devices.
3. Outlook, Hotmail and Yahoo! Mail are forms of SaaS.
Which of the statements given above are correct? (A) 1 and 2 only (B) 2 and 3 only (C) 1 and 3 only (D) 1, 2 and 3

Accepted Answer

(D) 1, 2 and 3 — Correct. SaaS allows interface customisation, is accessible via mobile devices, and web-based email services are standard SaaS examples.

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