Miscellaneous: UPSC Previous Year Questions (Science and Technology)

Explanation

Alternative Powertrain Vehicles: Vehicles using propulsion systems other than conventional petrol or diesel internal combustion engines (ICEs), focusing on sustainable transport via electricity, hydrogen, or hybrid systems. Full Battery Electric Vehicles (BEVs): Powered solely by electricity in rechargeable battery packs, using electric motors, no ICE, fuel tank, or exhaust. Key Features:

Zero tailpipe emissions, reducing environmental impact. Efficiency depends on electricity source (renewable vs. fossil fuels). Examples: Tesla Model 3 (2017), Tata Nexon EV (2020). Hydrogen Fuel Cell Vehicles (FCEVs): They generate electricity via hydrogen-oxygen electrochemical reaction in fuel cell stack, powering electric motors; emit water vapor, heat. Key Features:

Zero-emission, suited for long-range, heavy-duty applications with fast refueling. Examples: Toyota Mirai (2014), Hyundai Nexo (2018). Fuel Cell Electric Hybrid Vehicles (FCE-HVs): They integrate hydrogen fuel cells and rechargeable batteries to power electric motors, using regenerative braking (turns kinetic energy into electricity by reversing the process that drives the car forward.) Key Features:

Combine fuel cell range, battery power for efficiency. Examples: Toyota, Honda prototypes (2020s). Hence, option (c) is correct.

Explanation

In electric vehicle lithium-ion batteries, cobalt, lithium, and nickel form cathodes determining energy density, lifespan, cost, and performance. Graphite is used exclusively in anodes, not cathodes. Electrolytes enable lithium ion movement, while separators prevent short circuits, allowing ion flow. Lithium-ion cell types are generally recognised by the cathode material. Some of the most common lithium-ion variants (based on cell chemistry) are NMC (Lithium nickel manganese cobalt), LFP (Lithium ferro (iron) phosphate), NCA (Lithium nickel cobalt aluminium oxide), LMO (Lithium manganese oxide) and LCO (Lithium cobalt oxide). Element-Wise Analysis Cobalt: Enhances thermal stability, extends lifespan in LCO, NMC, NCA. Used in smartphones, laptops (LCO), EVs Challenges: Expensive, toxic, 70% sourced from Democratic Republic of Congo (DRC), raising ethical concerns. Lithium: Critical for cathode (LiCoO₂, LiNiMnCoO₂, LiNiCoAlO₂, LiFePO₄) and electrolyte. Enables high voltage, sourced from Lithium Triangle (Chile, Argentina, Bolivia) and Australia. Nickel: Boosts energy density, range in NMC, NCA (80% of EV battery capacity, 2021). Supplied by Indonesia, Russia, Philippines. Challenge: Reduces thermal stability, needs cobalt, manganese. Graphite: Exclusive to anodes (28% of EV battery minerals), not cathodes. Natural/synthetic graphite intercalates lithium ions for conductivity, stability. China dominates anode-grade graphite. Research explores silicon anodes. Hence, option (c) is correct.

Explanation

Ethanol and urea can be produced via coal gasification, while nitroglycerine is not practically produced due to the lack of a viable glycerol synthesis pathway from syngas. Coal Gasification: It is a thermochemical process that converts coal into syngas (synthesis gas), a mixture of carbon monoxide (CO), hydrogen (H₂), carbon dioxide (CO₂), and methane (CH₄), through partial oxidation with oxygen and steam under high temperature (1000°C or more) and pressure. Syngas serves as a versatile chemical feedstock for producing fuels, fertilizers, and chemicals, supporting India’s National Coal Gasification Mission (2021) to gasify 100 million tonnes of coal by 2030 to reduce imports of natural gas, urea, and methanol. Ethanol: Production via Coal Gasification Process: Ethanol (CHOH) is produced from syngas through catalytic conversion (e.g., Fischer-Tropsch synthesis with rhodium-based catalysts) or microbial fermentation (e.g., using Clostridium ljungdahlii). Relevance: Syngas provides carbon monoxide and hydrogen, which are converted to ethanol as part of coal-to-liquids (CTL) processes. This supports India’s 20% ethanol blending policy (G20 Biofuel Policy) to reduce crude oil imports. Nitroglycerine: Feasibility via Coal Gasification Process: Nitroglycerine (CHNO), an explosive and pharmaceutical vasodilator, is produced by nitrating glycerol with nitric acid and sulfuric acid under controlled conditions. Relevance to coal gasification:

Syngas can produce hydrogen for ammonia via the Haber-Bosch process, which is used to make nitric acid. However, glycerol synthesis from syngas (e.g., via methanol-to-olefins or propylene pathways) is commercially unviable and not documented in coal gasification applications. While syngas can indirectly support nitric acid production, the glycerol required for nitroglycerine is not practically derived from coal gasification, making the process infeasible for industrial use. Urea: Production via Coal Gasification Process: Urea (CO(NH₂)₂) is produced by reacting ammonia (NH₃) with carbon dioxide (CO₂), both derivable from syngas. Hydrogen from syngas is used in the Haber-Bosch process to produce ammonia. Carbon monoxide in syngas is converted to CO via the water-gas shift reaction (CO + H₂O → CO₂ + H₂).

Explanation

Rare earth elements (REEs) are a group of 17 chemically similar metallic elements that are known for their high luster, high density, and unique magnetic, phosphorescent, and catalytic properties.

Statement 1 is correct: Rare earth elements such as europium, terbium, and yttrium are crucial for producing the bright, vivid colors in modern flat screens and monitors.

Statement 2 is correct: Many rare earth elements, like europium and terbium, have phosphorescent or luminescent properties, meaning they can absorb energy and emit light, which is used in various applications including displays.

Explanation

Pumped-storage hydropower (PSH) is primarily discussed in the context of long-duration energy storage. It is a type of hydroelectric power generation that stores excess electricity by pumping water from a lower reservoir to an upper reservoir during times of low energy demand. When energy demand is high, the stored water is released back down through turbines to generate electricity. This technology helps balance grid fluctuations, integrate renewable energy sources like wind and solar, and provide a reliable backup power supply.

Explanation

The exhaust pipe emission from Fuel Cell Electric Vehicles (FCEVs) powered by hydrogen is water vapour. These vehicles use hydrogen fuel cells to generate electricity through an electrochemical reaction between hydrogen and oxygen. The only by-product of this process is water (H₂O), which is released as vapour, making FCEVs a clean and environmentally friendly transportation option. Fuel cells are unique in terms of the variety of their potential applications; they can use a wide range of fuels and feedstocks and can provide power for systems as large as a utility power station and as small as a laptop computer.

Explanation

Green hydrogen is expected to play a prominent role in decarbonising heavy industries, including oil refineries, steel mills and fertiliser plants. Green hydrogen is produced by breaking down water in an electrolyser using only renewable energy, resulting in no carbon emissions. The production of fertiliser demands substantial energy, typically sourced from fossil fuels like natural gas. However, green hydrogen offers a promising alternative, serving either as an electricity source or directly utilised in the ammonia production process, which is crucial for manufacturing fertilizer. Oil refineries significantly contribute to greenhouse gas emissions through their energy-intensive operations and dependence on fossil fuels. However, integrating green hydrogen into refinery operations offers a viable solution to mitigate this impact by either substituting or complementing fossil fuels, thereby decreasing their carbon footprint. Hydrogen can play a vital role in refining procedures like hydrocracking and hydrotreating, enhancing fuel quality by eliminating impurities. The steel industry contributes substantially to worldwide carbon emissions. However, the adoption of green hydrogen presents an opportunity to address this issue by serving as a replacement for coal or coke as a reducing agent in the steelmaking process. Green hydrogen enables the Direct Reduced Iron (DRI) process, producing environmental -friendly or low-carbon steel. It can also support heat and electricity generation, further cutting emissions.

Explanation

Statement 1 is correct: Finely ground basalt rock is dispersed across agricultural lands to expedite the natural absorption of carbon dioxide from the atmosphere. This is known as enhanced rock weathering, where silicate minerals react with CO₂, forming stable carbonates and reducing atmospheric carbon, as well as improving the fertility of the soil.

Statement 2 is correct: This method, referred to as ocean alkalinity enhancement, encompasses the addition of lime (calcium oxide or calcium hydroxide) to the oceans to elevate their alkalinity. By doing so, it boosts the oceans’ ability to absorb and retain carbon dioxide from the atmosphere, thus assisting in carbon sequestration.

Statement 3 is correct: The process known as carbon capture and storage (CCS) involves capturing carbon dioxide emissions from industrial processes and storing them underground. Abandoned subterranean mines can be utilised as viable storage sites, where the captured carbon dioxide is injected into these locations as carbonated waters.

Explanation

An accelerometer is an electromechanical device used to measure acceleration forces. These forces may be static like the continuous force of gravity or dynamic force to sense movement or vibrations.

Statement 1 is correct: Upon a collision, the crash sensor, typically an accelerometer, transmits a signal to the airbag control unit to deploy the airbags almost immediately.

Statement 2 is correct: Accelerometers in laptops protect hard drives from damage. If the laptop were to suddenly drop while in use, the accelerometer would detect the sudden free fall and immediately turn off the hard drive to avoid hitting the reading heads into the hard drive platter.

Statement 3 is correct: Accelerometer is used in smartphones as it detects the rotation of their display between portrait and landscape mode depending on the tilt of the phone.

Explanation

Statement 1 is correct: The use of biofilters to remove toxins from wastewater and waste gases has advanced in recent decades. In order to remove contaminants from a fluid stream, biofilters fix microorganisms to an inorganic/organic medium (carrier), which has the ability to break down a wide range of chemicals. By removing uneaten fish feed, they additionally perform waste treatment.

Statement 2 is correct: By constructing a biofilter correctly, it is possible to regulate ammonia and nitrite concentrations at levels safe for fish. Through the biofiltration process, ammonia nitrogen is converted into nitrite nitrogen, which is subsequently transformed into less harmful nitrate nitrogen, ensuring a conducive environment for fish.

Statement 3 is incorrect: Biofilters do not increase phosphorus as a nutrient for fish in water. Phosphorus (P) is actually removed by biofilters to prevent eutrophication in waters.