Defence, nuclear & energy technology

Answer: (c) I, II and III

Direct air capture (DAC) pulls CO2 straight out of ambient air. The captured CO2 can be stored underground, which removes it from the atmosphere, or used as a carbon feedstock for products such as food and beverages, chemicals and some plastics, and, combined with hydrogen, for synthetic aviation fuel. All three statements describe real uses.

• ✓ I Capturing CO2 from the air and storing it permanently removes it from the atmosphere; this is carbon removal by sequestration.
• ✓ II Air-captured CO2 can serve as a climate-neutral feedstock for a range of products, from food and beverages to chemicals, and some plastics are among the CO2-based products.
• ✓ III Air-captured CO2 combined with hydrogen is used to make synthetic hydrocarbon fuels, notably for aviation.

Remember · Direct air capture takes CO2 from ambient air: store it (carbon removal) or use it (food and beverages, chemicals, plastics, and synthetic fuels made with hydrogen).

Question and answer: UPSC's official GS Paper I (2025, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (c) All the three

An alternative powertrain vehicle is one driven by something other than a conventional internal combustion engine running on petrol or diesel. Battery-electric cars, hydrogen fuel-cell cars and fuel-cell hybrids that pair a fuel cell with an electric drive all fit, so all three are alternative powertrain vehicles.

• ✓ I A full battery electric vehicle has a battery charged from the grid and always operates in all-electric mode (US DOE Alternative Fuels Data Center); the World Bank lists battery electric vehicles among the alternative technologies countries are adopting.
• ✓ II A hydrogen fuel-cell vehicle is powered by hydrogen and produces no harmful tailpipe pollutants, unlike a conventional internal combustion engine vehicle; the World Bank treats it as another alternative to battery-powered vehicles.
• ✓ III A fuel cell-electric hybrid is built around a fuel cell supplying an electric motor, with a battery storing braking energy (US DOE), so it too replaces the conventional engine and counts as an alternative powertrain.

Remember · Alternative powertrains replace the conventional petrol/diesel engine: battery electric, hydrogen fuel cell and fuel cell-electric hybrid vehicles all count.

Question and answer: UPSC's official GS Paper I (2025, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 1 Oct 2026 (how we verify). Permalink · Report an error

Answer: (d) None

UAVs come in different designs with different abilities. Fixed-wing UAVs fly like aeroplanes and need a launcher and a landing device, while hovering and vertical take-off and landing belong to multirotor and hybrid VTOL types. Drones can also run on gasoline or hydrogen fuel cells, not only batteries. So none of the three 'all types' claims is correct.

• ✗ I Fixed-wing UAVs get lift from a rigid wing like an aeroplane and need launch infrastructure and a landing device; vertical landing is a feature of multirotor and VTOL types.
• ✗ II Hovering capability is one of the ways drones differ. Multirotors hover; fixed-wing UAVs, which rely on forward flight for lift, do not.
• ✗ III Battery power is only one option. Gasoline-powered drones give longer flight times, and fuel-cell (hydrogen) UAVs also exist, so not every UAV is battery-only.

Remember · UAV types differ: multirotor and VTOL can hover and land vertically, fixed-wing cannot; power may be battery, gasoline or hydrogen fuel cell.

Question and answer: UPSC's official GS Paper I (2025, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (b) These are explosives in military weapons

CL-20, HMX and LLM-105 are all high explosives, the kind packed into warheads and other military munitions. None of them is a refrigerant or a fuel; they release energy by detonating, not by burning steadily with oxygen from outside.

• ✓ (b) DRDO's High Energy Materials Research Laboratory, Pune, made CL-20 in the laboratory as a more powerful explosive than HMX, which fills most warheads. LLM-105 is also an explosive, an insensitive one whose performance lies between HMX and TATB.
• ✗ (c) Cruise missiles are propelled by ordinary fuels burnt in an engine. These three compounds sit in the warhead, not in the fuel tank.
• ✗ (a) Hydrofluorocarbon (HFC) refrigerants are gases used for cooling; these three are solid explosive compounds, so they have nothing to do with refrigeration.
• ✗ (d) Rocket propellants are designed to burn in a controlled way. These compounds are designed to detonate and are used as explosive fills.

Remember · CL-20 (most powerful of the three), HMX and LLM-105 (an insensitive explosive) are high-energy explosives for warheads, not fuels or refrigerants.

Question and answer: UPSC's official GS Paper I (2025, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (b) Only two

Two of the three pairs are correct. The Indian Coast Guard describes the Dornier-228 as a multi-mission maritime patrol aircraft, and the C-17 Globemaster III is a military transport, but the IL-76 is a strategic airlift aircraft, not a supersonic combat aircraft.

• ✓ I The Dornier-228 bought for the Indian Coast Guard is fitted with maritime patrol radar and an electro-optic infra-red device to strengthen aerial surveillance of maritime areas.
• ✗ II The IL-76 (Gajraj) is described by the Ministry of Defence as an Indian Air Force strategic airlift aircraft. It is a transporter, not a supersonic combat aircraft.
• ✓ III The C-17 Globemaster III was inducted into the Indian Air Force in 2013 to strengthen its strategic airlift.

Remember · Dornier-228: maritime patrol (Coast Guard). IL-76: strategic airlifter. C-17 Globemaster III: strategic military transport.

Question and answer: UPSC's official GS Paper I (2025, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 1 Oct 2026 (how we verify). Permalink · Report an error