DAY – 58 : Insta 75 Days Revision Plan-2026 : SCIENCE & TECHNOLOGY

Answer: (c)

Explanation

Underground Coal Gasification (UCG) is an industrial process which converts coal into product gas (syngas) while it remains in the seam. It is often viewed as a way to utilize coal resources that are otherwise difficult or uneconomical to extract through traditional mining.

• Statement 1 is correct: UCG is an in-situ (on-site) process. Oxidants (usually air, oxygen, or steam) are injected into the coal seam through a borehole. This triggers a controlled combustion/gasification process that converts deep or non-minable coal into syngas (a mixture of hydrogen, carbon monoxide, methane, and carbon dioxide). This gas is then extracted through a separate production well.
• Statement 2 is correct: Because the gasification happens underground, there is no physical mining of the coal. This eliminates the need for large-scale excavations and heavy machinery associated with open-cast or underground mining. Furthermore, the coal ash remains in the underground cavity created by the gasification, significantly reducing the environmental challenge of surface coal ash handling and disposal.

The produced syngas can be used for power generation, as a chemical feedstock for producing fertilizers (like urea), or converted into liquid fuels (Gas-to-Liquids).

Answer: (a)

Explanation: Statement 1 is incorrect— it reduces irrigation needs (3–4 cycles vs 5–6). Statement 2 is correct (trials on wheat, guar gum, bajra, chickpea). Statement 3 is incorrect — it is a low-cost, simple application, not machinery-intensive. Hence, only one correct.

Context: Researchers at the Central University of Rajasthan (CUoR) successfully grew wheat on desert land in Ajmer using ‘soilification’ technology.

About Soilification Technology:

• What it is?

• • A biotechnology-based method that transforms loose desert sand into soil-like medium suitable for farming.
  • Uses indigenous bioformulations and polymers to improve fertility and water retention.

• How it works?

• • Polymer application: Cross-links sand particles, converting loose sand into structured soil.
  • Bioformulation: Enhances microbial activity, improving nutrient cycling and soil health.
  • Water retention: Creates a binding effect, lowering irrigation requirements.
  • Stress resistance: Strengthens plant tolerance to heat and arid conditions.
  • Crop adaptability: Successfully trialled on wheat, bajra, guar gum, and chickpea.

• Key Features:

• • Water efficient: Reduced irrigation cycles (3–4 vs. 5–6 in normal farming).
  • High yield ratio: Wheat yield recorded at 1:20 (seed to harvest), twice the output of untreated desert land.
  • Low input cost: Uses locally available bio-agents and simple application techniques.
  • Eco-restorative: Converts barren deserts into cultivable farmland without heavy machinery.

Answer: (b)

Explanation

A Digital Signature is a mathematical technique used to validate the authenticity and integrity of a digital document, message, or software. It is the digital equivalent of a handwritten signature or stamped seal, but it offers far more inherent security.

• Statement 1 is correct: Digital signatures provide three core security features:
  • Authentication: Confirms the identity of the signer.
  • Integrity: Ensures the document has not been altered since it was signed.
  • Non-repudiation: Prevents the signer from later denying that they signed the document.
• Statement 2 is incorrect: Digital signatures are based on Asymmetric Cryptography (Public Key Infrastructure). They use a pair of keys:

• 1. A Private Key, which is kept secret by the signer and used to create the signature.
  2. A Public Key, which is shared with everyone and used by the recipient to verify the signature. The same key is not used for both signing and verification.

• Statement 3 is correct: In India, Digital Signatures are legally recognized under Section 5 of the Information Technology (IT) Act, 2000. This law gives digital signatures the same legal status as physical signatures for most legal and commercial purposes.

Answer: (d)

Explanation:
LiDAR, or Light Detection and Ranging, is an advanced remote sensing technology. It measures the distance to a target by sending laser pulses and recording the time taken by the reflected pulses to return to the sensor.

Statement 1 is correct: LiDAR uses light in the form of pulsed laser to measure distances to the Earth’s surface. These laser pulses, along with other data recorded by the system, help generate accurate three-dimensional information about the shape and surface features of the Earth.

Statement 2 is correct: LiDAR is widely used for preparing high-resolution Digital Elevation Models (DEMs). It measures the time taken by laser pulses to return after hitting the ground or objects such as trees and buildings. This creates a dense “point cloud” of data, which helps in accurate 3D mapping of the terrain.

Statement 3 is correct: Specialised LiDAR techniques, such as Differential Absorption LiDAR (DIAL), can be used to measure atmospheric components. By using different wavelengths of light, these techniques can help detect gases such as carbon dioxide (CO₂), sulphur dioxide (SO₂) and methane (CH₄) in the atmosphere.

Therefore, all three statements are correct.

Answer: (c)

Explanation:

Pair 1 is correctly matched: Flue-gas desulfurization (FGD) refers to a set of technologies used to remove sulphur dioxide (SO₂) from the exhaust flue gases of fossil-fuel-based power plants. The most common method involves scrubbing the flue gas with an alkaline sorbent, such as lime or limestone, which reacts with SO₂ to form gypsum.

Pair 2 is correctly matched: Selective catalytic reduction (SCR) is an advanced emission control technology used to reduce nitrogen oxides (NOₓ). It works by injecting a reducing agent, usually ammonia or urea, into the flue gas stream. In the presence of a catalyst, NOₓ is converted into nitrogen (N₂) and water (H₂O).

Pair 3 is correctly matched: An electrostatic precipitator (ESP) is a filtration device used to remove fine particles such as dust and smoke from a flowing gas. It applies a high-voltage electrostatic charge to particulate matter (PM), after which the charged particles are collected on metal plates.

Therefore, all three pairs are correctly matched.

Answer: (c)

Explanation:
Statement 1 is incorrect: BEVs are generally more energy-efficient than FCEVs when the full fuel cycle is considered. In BEVs, electricity is directly stored in batteries and used to run the motor. In FCEVs, energy is lost during hydrogen production, compression, transport, storage and conversion back into electricity inside the fuel cell.

Statement 2 is correct: FCEVs generally offer a higher driving range than many BEVs, mainly because hydrogen has high energy density and can support longer-distance travel.

Statement 3 is correct: Batteries used in BEVs are heavy and usually take longer to recharge compared to hydrogen refuelling, which can be done in a few minutes.

Therefore, only statements 2 and 3 are correct.

Answer: (d)

Explanation:
Compressed Biogas (CBG) is a purified and compressed form of biogas produced through the anaerobic digestion of organic waste materials.

Process: Raw biogas usually contains methane, carbon dioxide and small traces of gases such as hydrogen sulphide. To produce CBG, raw biogas is purified by removing carbon dioxide (CO₂), hydrogen sulphide (H₂S) and other impurities.

Composition: After purification, the methane content of CBG is increased to more than 90%, making it chemically similar to Compressed Natural Gas (CNG).

Utility: Due to its similar calorific value and fuel properties, CBG can be used as a substitute for CNG in automotive, industrial and commercial applications, without requiring major modifications in engines or burners.

Answer: (d)

Explanation:
Nanotechnology involves the manipulation of matter at the atomic, molecular and supramolecular levels, usually in the range of 1 to 100 nanometres. At this scale, materials show unique physical, chemical and biological properties that are different from their bulk form.

Statement 1 is correct: In the textile industry, nanoscale additives are used to improve the quality of fabrics. For example, silver nanoparticles can provide antimicrobial properties and help prevent bacterial growth and odour. Other nanomaterials can make fabrics more resistant to stains, water and wrinkling.

Statement 2 is correct: Nanoscale thin films are widely used in optics and electronics. They can make surfaces water-repellent and can also block specific wavelengths such as ultraviolet or infrared radiation. Such coatings are useful in eyeglasses, computer screens, camera displays and other optical devices.

Statement 3 is correct: Nanostructured ceramic coatings can be tougher and more wear-resistant than conventional coatings. Their nanoscale structure helps improve strength, heat resistance and durability, making them useful for machine parts, aircraft engines and cutting tools.

Therefore, all three statements are correct.

Answer: (c)

Explanation:
Waste-to-Energy (WtE) includes different technologies that recover energy from municipal solid waste, agricultural residues and other organic waste. It is an important part of waste management and the circular economy.

Statement 1 is correct: The production of biofuel from organic waste can be carbon-negative under certain conditions. For example, anaerobic digestion of organic waste produces biogas and prevents the uncontrolled release of methane from rotting waste in landfills. Since methane is a powerful greenhouse gas, its capture and use as energy can reduce net emissions. In some cases, if the by-products such as bio-slurry or biochar are used to store carbon in the soil, or if carbon capture and storage is applied, the overall process can become carbon-negative.

Statement 2 is correct: WtE plants, especially incineration-based plants, generate bottom ash and fly ash after combustion. This residue ash can be used in construction activities, such as manufacturing cinder blocks, bricks and road sub-base material, after proper treatment and safety checks. This reduces the burden of ash disposal in landfills and also lowers the demand for natural construction materials.

Therefore, both statements are correct.

Answer: (a)

Explanation:
Thorium-232 is considered important for India’s future nuclear energy programme, especially in the context of the third stage of India’s three-stage nuclear power programme. It has some advantages over the conventional uranium-based fuel cycle, though it also has certain technical challenges.

Statement 1 is correct: In a uranium-based fuel cycle, neutron capture by uranium-238 can lead to the formation of long-lived transuranic elements such as plutonium, americium and curium. In comparison, thorium-based fuel cycles generally produce much smaller quantities of such long-lived transuranic waste. This makes thorium attractive from the point of view of radioactive waste management.

Statement 2 is correct: Thorium is more abundant in nature than uranium. It is often estimated to be around three to four times more abundant in the Earth’s crust. For India, this is particularly important because India has large thorium reserves, especially in monazite sands found in coastal regions such as Kerala and Odisha, while domestic uranium reserves are comparatively limited.

Statement 3 is incorrect: Thorium-based fuel cycles are not easier to weaponize. In fact, they are generally considered more proliferation-resistant than uranium-based fuel cycles. Thorium itself is fertile, not fissile, and must be converted into uranium-233 to be used as fuel. Also, uranium-233 is often contaminated with uranium-232, which emits strong gamma radiation and makes handling difficult and dangerous for weapons-related misuse.

Therefore, only statements 1 and 2 are correct.

Correct Answer: (a)

Detailed Solution:

The objective is to identify the specific person from Delhi. We have three unique individuals and three unique cities.

From Statement 1: We are explicitly told C is from Mumbai. This leaves two individuals, A and B, and two cities, Delhi and Kolkata. The statement further adds that B is not from Kolkata. Since Kolkata is the only other option besides Delhi, B must be from Delhi. Consequently, A must be from Kolkata. This provides a definitive answer using only Statement 1.

From Statement 2: We are told A is not from Delhi. This means A could be from either Mumbai or Kolkata. However, we have no information regarding the locations of B or C. Without knowing C’s city, we cannot narrow down whether B or C is the one from Delhi. Thus, Statement 2 alone is insufficient.

Therefore, Statement 1 alone is sufficient.

Correct Answer: (a)

Detailed Solution:

To determine if P is divisible by 12, it must be divisible by its factors 3 and 4 (since 3 and 4 are co-prime).

From Statement 1: P is the product of four consecutive positive integers (n, n+1, n+2, n+3). In any set of four consecutive integers, one must be a multiple of 4 and at least one must be a multiple of 3. Furthermore, at least two of the numbers must be even. The product of n consecutive integers is always divisible by n!. Thus, the product of 4 consecutive integers is always divisible by 4!, which is 24. Since P is divisible by 24, it is fundamentally divisible by 12. Statement 1 is sufficient.

From Statement 2: P is divisible by 3. This does not provide information about divisibility by 4. For instance, if P = 9, it is divisible by 3 but not 12. If P = 36, it is divisible by both. Since we cannot reach a single conclusion, Statement 2 is insufficient.

Correct Answer: (c)

Detailed Solution:

Take Point Y as (0, 0).

• From Y, move 6 km East → Z = (6, 0)
• From Z, move 8 km South → W = (6, −8)

Distance between Y and W:
= √[(6)² + (−8)²]
= √(36 + 64)
= √100
= 10 km

Correct Answer: (d)

Detailed Solution:

Take starting point as (0, 0).

• Move 20 m East → (20, 0)
• Turn right (South), move 10 m → (20, −10)
• Turn left (East), move 10 m → (30, −10)

Now facing East.

• Turn 135° left → direction becomes North-West
• Move 30√2 m:
  • x decreases by 30
  • y increases by 30

Final position = (30 − 30, −10 + 30) = (0, 20)

Since x = 0 and y is positive, the person is due North of the starting point.

Correct Answer: (c)

Detailed Solution:

(a) is incorrect as the passage suggests regulations “lag behind,” which implies they are struggling to keep pace, but does not equate to being “entirely ineffective.”

(b) is incorrect because the passage explicitly notes that the issue has evolved beyond targeted advertising, highlighting a much deeper impact on reality and democracy.

(c) is the correct inference. The passage concludes that these algorithms create “filter bubbles” and “digital echoes” that “threaten the deliberative nature of democracy.” By calling it a “silent curation of reality,” the author implies that the algorithmic manipulation of information is a systemic threat to how democratic societies function.

(d) is incorrect because the text attributes the construction of these bubbles to “algorithmic profiling” and the algorithms themselves, rather than user behavior or choice.