Science & Technology

Correct answer: (D) All four

Distributed Energy Resources (DERs) are small-scale power generation or storage units located close to where electricity is used, connected to the distribution grid rather than large central plants. Battery storage, biomass generators, fuel cells, and rooftop solar PV units all qualify because each generates or stores energy in a decentralised manner. Hence all four are DERs, making option (d) correct.

Correct answer: (B) 2 and 3 only

Statement 1 is false: RTGs are not fission reactors; they generate electricity from the heat released by the natural radioactive decay of an isotope using thermocouples, with no chain reaction. Statement 2 is true, as RTGs reliably power spacecraft onboard systems on deep-space missions (e.g., Voyager, Cassini). Statement 3 is true, since RTGs commonly use Plutonium-238, produced in connection with weapons/nuclear programmes. Hence only 2 and 3 are correct, option (b).

Correct answer: (D) Statement-I is incorrect, but Statement-II is correct

Statement I is incorrect: giant stars actually live much shorter lives than dwarf stars because they consume their nuclear fuel very rapidly. Statement II is correct, since giant stars, being far more massive and luminous, sustain a much higher rate of nuclear reactions. The faster fuel consumption is precisely why giants are short-lived, so Statement I is false while Statement II is true, giving option (d).

Correct answer: (A) Nitric oxide

Nitric oxide (NO) is synthesised in the human body (from arginine by nitric oxide synthase) and acts as a signalling molecule that relaxes the smooth muscle of blood vessel walls, causing vasodilation and increased blood flow. This is the basis of drugs like nitroglycerin. Nitrous oxide (laughing gas), nitrogen dioxide, and nitrogen pentoxide are not body-synthesised vasodilators, so option (a) is correct.

Correct answer: (B) Only two

Radar works by transmitting radio waves and detecting their reflections, so it can monitor precipitation (weather/Doppler radar) and track the movement/migration of animals and birds. Detecting narcotics on passengers relies on chemical sensors, X-ray/scanners, and sniffer techniques rather than radar. Thus radar applies to only two of the listed activities, making option (b) correct.

Correct answer: (D) None

None of the listed aircraft is a fifth-generation fighter. The Rafale is a 4.5-generation multirole jet, the MiG-29 is a fourth-generation fighter, and the indigenous Tejas Mk-1 is a fourth/4.5-generation aircraft. Fifth-generation fighters (with stealth, supercruise, and advanced sensor fusion) include jets like the F-35 or Su-57, so the answer is None, option (d).

Correct answer: (A) 1 only

Hydrogels are water-swollen polymer networks whose best-known application is controlled drug delivery, where they release medication gradually in patients (statement 1). As per the official key, they are not the answer for mobile air-conditioning systems or industrial lubricant preparation, so only statement 1 is accepted, giving option (a).

Correct answer: (D) Water vapour

In a hydrogen fuel cell, hydrogen combines with oxygen from the air to produce electricity, and the only tailpipe emission is water (water vapour). This is why hydrogen fuel cell electric vehicles are considered zero-emission at the point of use. Hence option (d), water vapour, is correct.

Correct answer: (C) Long duration energy storage

Pumped-storage hydropower is a long-duration energy storage technology: during surplus/off-peak periods, water is pumped up to an upper reservoir, and during peak demand it is released back down through turbines to regenerate electricity. It effectively acts as a large grid-scale battery, so it is discussed in the context of long duration energy storage, option (c).

Correct answer: (D) Wastewater treatment technologies

Membrane Bioreactors (MBRs) combine biological treatment (activated sludge) with membrane filtration (microfiltration/ultrafiltration) to treat wastewater, producing high-quality, clean effluent in a compact system. They are a key technology in modern sewage and effluent treatment plants. Therefore they are discussed in the context of wastewater treatment technologies, option (d).

Correct answer: (C) Metaverse

The Metaverse denotes an interoperable network of persistent, shared 3D virtual worlds accessed simultaneously by many users, where they can own and exert property rights over virtual items (often via NFTs/blockchain). This exactly matches the description, so option (c) is correct; big data analytics and cryptography refer to unrelated concepts.

Correct answer: (C) Statement-I is correct but Statement-II is incorrect

Statement-I is correct but Statement-II is incorrect. India does depend on coal for the bulk of its electricity despite having uranium reserves, because its nuclear capacity is limited. Statement-II is false: reactor-grade uranium for power generation needs to be enriched only to about 3-5% U-235; enrichment to 60% or more is associated with weapons-grade/high-enrichment applications, not routine electricity production.

Correct answer: (C) Honeybees

Honeybees perform the waggle dance, first decoded by Karl von Frisch. A returning forager moves in a figure-eight pattern on the comb; the angle of the straight 'waggle' run relative to vertical encodes the direction to the food relative to the sun, and the duration encodes the distance.

Correct answer: (D) All four

All four statements are correct. Mushrooms/fungi can be medicinal (e.g. Reishi, Cordyceps, penicillin sources), psychoactive (psilocybin mushrooms), insecticidal (entomopathogenic fungi like Beauveria and Metarhizium kill insects), and bioluminescent (species like Mycena and Omphalotus glow in the dark). Hence the answer is all four.

Correct answer: (C) All three

All three are correct. Extremophile microorganisms exist across these conditions: thermophiles/hyperthermophiles grow above 100 degrees C near hydrothermal vents; psychrophiles grow below 0 degrees C in polar ice and brine; and acidophiles thrive in strongly acidic environments with pH below 3, such as acid mine drainage. Hence all three statements are valid.

Correct answer: (C) Only three

Only three are correct. Hydrofluorocarbons (HFCs), used as replacements for ozone-depleting CFCs, are employed in aerosols (as propellants), foam-blowing agents, and fire retardants/extinguishing agents, in addition to refrigeration. They are not used as lubricants, so lubricants is the odd one out, giving three.

Correct answer: (A) 1 only

The answer is '1 only'. Carbon fibres, valued for their high strength-to-weight ratio, are indeed used to make lightweight components for automobiles and aircraft, so statement 1 is correct. Statement 2 is false: carbon fibre can be recycled (for example by pyrolysis that recovers the fibres from composite waste), so the claim that it cannot be recycled is wrong. Only statement 1 holds.

Correct answer: (C) All three

The answer is 'All three'. An accelerometer senses changes in motion/acceleration and is essential in all three cases: sudden deceleration in a crash triggers airbag deployment, sensing a laptop's free fall parks the hard-drive heads to prevent damage, and detecting the tilt/orientation of a smartphone switches the display between portrait and landscape. Each function relies on accelerometer data, so all three are correct.

Correct answer: (B) Only two

In a Recirculating Aquaculture System the biofilter is the site of nitrification, where nitrifying bacteria (Nitrosomonas, Nitrobacter) convert toxic ammonia excreted by fish first into nitrite and then into far less toxic nitrate, so statement 2 is correct. Biofilters are broadly part of the water-treatment stage that keeps dissolved wastes in check, so statement 1 is accepted as correct. Statement 3 is false: biofilters do not add phosphorus as a nutrient, and excess phosphorus is a pollutant, not a benefit. Two statements are correct.

Correct answer: (A) Only one

Only the Pulsar pair is right: pulsars are rapidly rotating neutron stars formed when massive stars exhaust their fuel and collapse. The other two are swapped: Cepheids are variable stars that brighten and dim periodically (used as cosmic distance markers), not clouds; and Nebulae are the giant clouds of dust and gas. Hence only one pair is correctly matched.

Correct answer: (D) Japan

Japan operates the Quasi-Zenith Satellite System (QZSS), nicknamed 'Michibiki', a regional satellite navigation system that augments GPS over the Asia-Oceania region. Among the options only Japan has its own such system; India has NavIC/IRNSS, but Australia, Canada and Israel do not run independent navigation constellations.

Correct answer: (D) Neither 1 nor 2

Both statements are false. Statement 1 reverses the facts: ballistic missiles are rocket-powered only in the boost phase and then follow a free-fall ballistic arc, while cruise missiles are typically jet-propelled and fly at sustained (often subsonic) speeds. Statement 2 also swaps the two: Agni-V is a long-range solid-fuelled intercontinental ballistic missile, whereas BrahMos is a supersonic cruise missile. Neither statement is correct.

Correct answer: (C) All three

All three uses are valid. Green hydrogen (produced by electrolysis using renewable power) can be burned directly as a fuel in internal-combustion engines, can be blended into natural-gas pipelines for heat and power, and can feed hydrogen fuel cells that generate electricity to run vehicles. Hence all three statements are correct.

Correct answer: (A) Controlling the viral diseases spread by mosquitoes

The Wolbachia method controls mosquito-borne viral diseases such as dengue, Zika and chikungunya. Mosquitoes (Aedes aegypti) are infected with the naturally occurring Wolbachia bacterium, which blocks the transmission of these viruses; the released mosquitoes then spread Wolbachia through the wild population, reducing disease transmission.

Correct answer: (A) Collecting DNA samples from air in a habitat at one go

Aerial metagenomics refers to collecting environmental DNA (eDNA) directly from air in a habitat in one sampling, then sequencing it to identify the many organisms whose genetic traces are suspended in that air. It is a biodiversity-monitoring technique, so option (a), collecting DNA samples from air at one go, best captures it.

Correct answer: (A) Studying the evolutionary relationships among various species of fauna

Microsatellites are short tandemly repeated DNA sequences that are highly polymorphic between individuals and species. Because their variation reflects genetic distance, they are widely used as molecular markers to study evolutionary and phylogenetic relationships among species (as well as in population genetics and DNA fingerprinting). Hence option (a) is correct.