Prelims Mantra (Practice Questions) (12/03/2026)

Answer: B

Explanation:

Bioenergy can come from multiple biomass sources, not only agricultural residues.

• • Statement 1 is incorrect: Bioenergy is not produced only from agricultural crop residues. It is derived from a wide variety of organic materials, including wood and forest residues, animal manure, municipal solid waste, food processing waste, and microorganisms like algae.
  • Statement 2 is correct: Second-generation (2G) biofuels are specifically designed to use non-food biomass. This includes lignocellulosic materials such as straw, husks, wood chips, and dedicated energy crops like switchgrass, which do not compete with food security.
  • Statement 3 is correct: Developing bioenergy infrastructure provides a commercial incentive for farmers to collect and sell surplus crop residues (like paddy straw) instead of burning them in open fields. This helps mitigate air pollution and greenhouse gas emissions.

Answer: D

Explanation:

• • Statement 1: Correct. According to the IPCC, as glaciers melt, the volume of water running downhill initially increases (often referred to as “peak water”). However, as the glacier shrinks significantly, this supply eventually diminishes, leading to a long-term decline in river discharge.
  • Statement 2: Correct. Black carbon fine soot from fossil fuel and biomass burning absorbs sunlight and reduces the albedo (reflectivity) of snow. When deposited on glaciers, it warms the surface and significantly accelerates melting.
  • Statement 3: Correct. Himalayan glaciers are the “Water Towers of Asia.” They provide the headwaters for ten major river systems, including the Indus, Ganges, and Brahmaputra, directly influencing the water security of over a billion people.

Answer: A

Explanation:

• • I-C: Aadhaaruses de-duplicated biometric data (fingerprints and iris scans) to ensure that each individual has a unique, non-replicable digital identity.
  • II-A: UPIrelies on Virtual Payment Addresses (VPAs) (e.g., name@bank) to enable instant, interoperable money transfers between different banks without needing account numbers.
  • III-B: DigiLockeruses asymmetric encryption to securely share and verify URI links (Uniform Resource Identifiers) of official documents directly from the original issuing authority to the requester.

Answer: A

Explanation:

Lithium belongs to alkali metals (Group 1), not transition metals.

• • Statement 1: Correct. Lithium is primarily extracted from two types of deposits: continental brines (found in salt flats or “salars,” notably in the “Lithium Triangle” of Chile, Argentina, and Bolivia) and hard-rock minerals (such as spodumene found in pegmatite rocks, with Australia being a leading producer).
  • Statement 2: Correct. Lithium-ion batteries function through a process called intercalation, where lithium ions move from the negative electrode (anode) to the positive electrode (cathode) during discharge, and back to the anode when charging.
  • Statement 3: Incorrect. In the periodic table, Lithium (atomic number 3) is an alkali metal (Group 1), not a transition metal. Transition metals are found in the d-block (Groups 3 to 12).

Answer: A

Explanation:

Hydrogen combustion produces water vapour, not carbon dioxide.

• • Statement 1: Correct. Hydrogen has an exceptionally high gravimetric energy density (energy per unit mass), approximately 120–142 MJ/kg. This is nearly three times higher than conventional fossil fuels like gasoline (~44–46 MJ/kg) or natural gas (~55 MJ/kg).
  • Statement 2: Correct. Green hydrogen is specifically defined by its production method: the electrolysis of water (splitting
  • into hydrogen and oxygen) using electricity from renewable sources like solar or wind power.
  • Statement 3: Incorrect. When pure hydrogen is burned (combusted) in the presence of oxygen, the primary by-product is water vapor and heat. It does not produce carbon dioxide because there is no carbon in the fuel itself. (Note: If burned in air, trace amounts of nitrogen oxides (NOx) may form, but not.

Answer: D

Explanation:

• • Statement 1 is correct: IN-SPACe acts as the single-window, autonomous nodal agency under the Department of Space. It is responsible for authorising and supervising all space activities by Non-Governmental Entities (NGEs), including launches and ground stations.
  • Statement 2 is correct: NewSpace India Limited (NSIL) is the commercial arm of ISRO. Its mandate includes commercialising space assets and enabling the mass production of launch vehicles like the PSLV through Indian industry partnerships.
  • Statement 3 is correct: The Indian Space Policy 2023 formally redefines ISRO’s role. It directs ISRO to move away from routine operational activities (like satellite manufacturing and launches) to focus on advanced Research & Development (R&D), deep-space exploration, and human spaceflight missions like Gaganyaan.

Answer: C

Explanation:

• • Statement 1 is correct: Ocean acidification is primarily caused by the absorption of atmospheric carbon dioxide into seawater. As humans burn fossil fuels and clear forests, the ocean acts like a sponge, absorbing about 30% of that extra.
  • Statement 2 is correct: When CO2 dissolves in water, it forms carbonic acid, which releases hydrogen ions. These hydrogen ions bond with carbonate ions to form bicarbonate. This “steals” the carbonate ions that marine calcifiers (like corals, oysters, and crabs) need to build and maintain their calcium carbonate shells and skeletons.

Answer: A

Explanation:

• • Statement I is correct: Silicon (Si) is the most widely used material in the semiconductor industry. Its abundance, low cost, and stable chemical properties make it the foundation for most modern electronic devices, including transistors, solar cells, and integrated circuits.
  • Statement II is correct: The utility of silicon as a semiconductor stems from the fact that its electrical conductivity is not fixed. Through a process called controlled doping the intentional introduction of specific impurities engineers can precisely modulate its conductivity by several orders of magnitude.
  • Statement II explains Statement I: The primary reason silicon is “widely used” as a semiconductor is specifically because its conductivity can be easily and precisely modified through doping. This adaptability allows for the creation of P-type and N-type layers, which are essential for building the P-N junctions that form the heart of all modern electronics.

Answer: D

Explanation:

• • Statement 1 is correct: These ecosystems are world-class carbon sinks. Their waterlogged, anaerobic soils prevent organic matter from decomposing quickly, allowing them to store up to 10 times more carbon per unit area than temperate or tropical terrestrial forests.
  • Statement 2 is correct: Corals are highly sensitive to turbidity (cloudy water). Because the mainland coasts of India (like the East Coast) receive heavy sediment from rivers like the Ganges and Godavari, major reef formations are restricted to the clear, oceanic waters of the Lakshadweep and Andaman & Nicobar Islands.
  • Statement 3 is correct: Unlike seaweed or algae, seagrasses are true flowering plants (angiosperms) with roots and seeds. Because they bury organic matter in oxygen-poor sediments, that carbon can remain trapped and stable for thousands of years if left undisturbed.

Answer: C

Explanation:

• • Statement 1 is correct: Hydraulic conductivity describes the ease with which water moves through soil. High conductivity in wetlands allows them to absorb large volumes of water during peak flows, regulating stream levels and recharging surrounding groundwater tables laterally.
  • Statement 2 is correct: Wetlands are famously known as the “Natural Kidneys” of the landscape. They improve water quality by filtering pollutants, transforming nitrogen through denitrification, and trapping heavy metals in their sediments and plant biomass.
  • Statement 3 is correct: Because wetland soils are often saturated with water, they create anaerobic (oxygen-poor) conditions. This prevents the rapid decomposition of organic matter, allowing wetlands especially peatlands to sequester and store carbon at much higher densities than terrestrial forests.
  • Statement 4 is incorrect: While wetlands produce their own organic matter (autochthonous), they are not “strictly” or “exclusively” so. Many wetlands are highly allochthonous, meaning they rely significantly on nutrients and organic matter brought in by external sources like rivers, runoff, or tides.