Miscellaneous: UPSC Previous Year Questions (Science and Technology)

Explanation

Graphene is a single layer of carbon atoms arranged in a hexagonal honeycomb lattice, making it the thinnest, strongest, and most conductive material known. It has remarkable applications in electronics, energy storage, and nanotechnology due to its high strength, flexibility, and conductivity.

Statement 1 is correct: Graphene, a two-dimensional, atomic-scale, honeycomb lattice is an allotrope of carbon in which one atom forms each vertex. It is the basic structural unit of other allotropes, including graphite, charcoal, carbon nanotubes and fullerenes. Graphene has remarkably good electrical conductivity.

Statement 2 is correct: It is often cited as about 100 times stronger than the strongest steel with a hypothetical thickness of 3.35°(approx.) which is equal to the thickness of a graphene sheet. Carbon atoms are linked together in a single layer to form the hexagonal structure that makes up graphene. Graphene is so much thinner than paper (a million times thinner), that it is actually regarded as two dimensional.

Statement 3 is incorrect: Graphene is a single layer (monolayer) of carbon atoms, not silicon, tightly bound in a hexagonal honeycomb lattice. It is an allotrope of carbon in the form of a plane of sp2-bonded atoms with a molecular bond length of 0.142 nanometres.

Statement 4 is correct: Graphene is often produced as a powder and as a dispersion in a polymer matrix. This dispersion is supposedly suitable for advanced composites, paints and coatings, lubricants, oils and functional fluids, capacitors and batteries, thermal management applications, display materials, etc. Graphene is often cited as a promising material for use as conducting electrodes in devices like touch screens, LCDs, and organic LEDs due to its excellent electrical conductivity and high transparency

Explanation

Lead poisoning is a toxic condition caused by the accumulation of lead in the body, typically through exposure to contaminated air, water, soil, or consumer products. It affects multiple organ systems, particularly the nervous system, and can lead to severe health issues such as cognitive impairment, developmental delays, and organ damage.

Option 1 and 3 are correct: Even after the stricter regulations, major sources of lead pollution include mining, smelting, manufacturing, and recycling, with the production of lead-acid batteries for automobiles accounting for over three-quarters of global lead usage. Other common sources of lead poisoning include lead-based paint, contaminated soil, children’s toys and jewelry, drinking water from lead pipes, workplace and hobby hazards (such as mining and smelting), lead-glazed ceramics, pottery, leaded crystal, imported candy, and mini blinds.

Option 2 and 4 are incorrect:

Pens and pencils are incorrect as modern pencils mostly contain graphite, not lead, and pens use regulated ink formulations. Hair oils and cosmetics are incorrect because most cosmetic products are strictly regulated to prevent lead contamination, with only rare exceptions in some traditional items.

Explanation

Cowpea, green gram, and pigeon pea are all versatile crops used in various agricultural practices. Cowpea is a leguminous plant that serves as a pulse, fodder, and green manure. Its seeds are harvested for food, while the plant’s leaves and stems are used as fodder for livestock. Additionally, cowpea is effective as green manure due to its ability to fix nitrogen in the soil, enhancing soil fertility. Green gram, primarily grown for its seeds, is mainly used as a pulse and also as fodder for animals. Although it can contribute to soil health, it is less frequently used as green manure compared to other legumes. Pigeon pea is similarly multifunctional, used as a pulse for consumption, fodder for livestock, and green manure to enrich soil. It plays a crucial role in improving soil fertility by fixing nitrogen. Overall, all three crops serve important roles in sustainable agriculture, with cowpea and pigeon pea being more widely used as green manure than green gram. Note: However, UPSC didn’t consider Pigeon Pea as suitable fit and marked option (a) as correct

Explanation

Statement 1 is correct: Thorium composes 0.0006% of the earth’s crust whereas Uranium composes 0.00018% of the earth’s crust, where a substantial amount of Uranium is found in dissolved seawater. Thus, Thorium(Th) is comparatively far more abundant in nature than uranium(U).

Statement 2 is correct: Uranium-233, produced from thorium, is generally considered to have higher energy output compared to natural uranium, with estimates suggesting it could produce significantly more energy per unit mass, though the exact ratio can vary depending on reactor design and conditions.

Statement 3 is correct: Thorium-based reactors generate less long-lived radioactive waste compared to uranium-based reactors. The waste from thorium has a lower proportion of transuranic elements like plutonium, which are highly radioactive and pose disposal challenges."

Explanation

Biologists studying various forms of life on Earth have identified a common characteristic among all living organisms. The matter within every living organism on Earth primarily consists of four chemical elements: hydrogen, oxygen, carbon, and nitrogen.

Option (b) is correct: Carbon, hydrogen, and nitrogen are the elements that were primarily responsible for the origin of life on Earth. These elements are fundamental in the formation of organic compounds, such as proteins, nucleic acids, and lipids, which are essential for life. The combination of carbon, hydrogen, and nitrogen forms the basis of amino acids, nucleotides, and other critical biomolecules involved in the origin of life on Earth.

Explanation

Capillarity (or capillary action) is the ability of a liquid to flow in narrow spaces, such as thin tubes or porous materials, without the assistance of external forces and even against gravity. It occurs due to the cohesion (attraction between liquid molecules) and adhesion (attraction between the liquid and solid surface), along with surface tension.

Statement 1 is correct: The oil in the wick of a lamp rises due to the capillary action of threads in the wick. Absence of capillarity would certainly make it difficult to use Kerosene lamps.

Statement 2 is incorrect: There is no capillary action in using a straw to consume the soft drink as the consumer applies additional pressure from the mouth to consume the soft drink.

Statement 3 is correct: A blotting paper soaks ink by the capillary action of the pores in the blotting paper. The blotting paper will not be useful without the capillarity phenomenon.

Statement 4 is correct: The root-hairs of plants draw water from the soil through capillary action. Therefore absence of capillarity phenomenon would adversely affect the growth of trees.

Explanation

In severe winter, a lake’s surface freezes while the bottom remains liquid due to the anomalous density behavior of water. Unlike most substances, water reaches its maximum density at 4°C, meaning that as it cools, denser water sinks while colder, lighter water (below 4°C) stays at the surface. When temperatures drop below 0°C, the surface water freezes first, forming an insulating ice layer that prevents further heat loss from the deeper water, keeping it in a liquid state. This phenomenon protects aquatic life, as it prevents the entire lake from freezing solid

Explanation

Microbial fuel cells (MFCs) are a bioelectrochemical technique, proposed to generate power using electrons from biological reactions in microorganisms.

Statement 1 is correct: These devices primarily use bacteria as catalysts to break down organic and inorganic substances, generating electrical current.

Statement 2 is incorrect: Microorganisms oxidise organic compounds, not inorganic substrates in the anode chamber, producing electrons and protons (reaction of anodes).

Statement 3 is correct: An MFC typically consists of two electrodes: the anode and the cathode. At the anode, bacteria decompose organic matter in wastewater, producing electrons and protons. The electrons travel through an external circuit to the cathode, generating electricity, while the protons move from the anode to the cathode. At the cathode, the electrons and protons combine with an electron acceptor, such as oxygen, to form water. As a result, MFCs can be implemented in wastewater treatment facilities to purify water and generate electricity.

Explanation

Moderator is used in a nuclear reactor for slowing down the neutrons produced during the fission reaction so that the chain reaction can be sustained. Due to its high moderating ratio and low neutron absorption cross section, heavy water makes a good moderator. Deuterium oxide, popularly known as heavy water (D₂O), is a hydrogen isotope with a mass double that of regular hydrogen and oxygen. However, In nuclear power reactors, heavy water can also be utilized as a coolant.

Explanation

Trans fatty acids (TFA) or trans fats are a form of unsaturated fat and come in both natural and artificial forms. Trans fats are the most harmful type of fats which can cause an adverse effect on a human body than any other dietary constituent.

Statement 1 is correct: Artificial trans fats are generated through an industrial process that adds hydrogen to liquid vegetable oils to form them more solid. That is hydrogen is made to react with the oil to produce fats that resemble pure ghee or butter. If items do not contain trans-fats, it means the food products are not made out of hydrogenated oils and animal fats/oils.

Statement 2 is incorrect: This is incorrect because not all animal fats contain trans fats. While small amounts of naturally occurring trans fats are found in some animal products, the harmful trans fats that raise cardiovascular risks are primarily from industrial hydrogenation, not from natural animal fats.

Statement 3 is correct: If items do not contain trans fats, it suggests that the oils used are less likely to harm the cardiovascular health of consumers, as oils associated with trans fats typically raise LDL (bad) cholesterol and lower HDL (good) cholesterol, contributing to plaque buildup in arteries and increasing the risk of heart attacks and strokes.