Science and Technology: UPSC Previous Year Questions (Prelims)

Explanation

Statement 1 is correct: Asteroids are primarily composed of rock and metal and are remnants from the early solar system. In contrast, Comets are made of ice, dust, and rocky material and originate from the Kuiper Belt or Oort Cloud.

Statement 2 is incorrect: Asteroids are predominantly located in the asteroid belt between Mars and Jupiter. Comets originate from distant regions of the solar system: short-period comets come from the Kuiper Belt beyond Neptune, and long-period comets originate from the distant Oort Cloud. They are not typically found between Venus and Mercury.

Statement 3 is correct: As comets approach the Sun, the heat causes their icy components to sublimate, forming a glowing coma and often a visible tail that points away from the Sun due to solar wind. Asteroids, being rocky and lacking volatile materials, do not exhibit such features.

Explanation

Statement 1 is correct: Geostationary Orbit is a type of geosynchronous orbit. The earth rotates in the same direction that satellites do. It lasts for roughly 24 hours and holds its place in relation to the earth.

Statement 2 is correct: The orbit must be nearly circular, ensuring that the satellite’s distance from Earth remains constant throughout its revolution. An elliptical orbit would cause the satellite to move closer and farther from Earth, disrupting its stationary position.

Statement 3 is correct: A Geostationary Orbit (GEO) is a special case of a Geosynchronous Orbit (GSO) where the satellite orbits exactly in the Earth’s equatorial plane (0° inclination). This ensures that the satellite appears fixed over a specific point on Earth.

Statement 4 is incorrect: Geostationary orbit is at an altitude of around 35,786 km.

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.

Explanation

Statement 1 is correct: An LED is a type of semiconductor light source with two leads. It is a p-n junction diode, which when turned on emits light. A fluorescent lamp is a low-pressure mercury-vapour gas-discharge light. In a CFL, an electric current is driven through a tube containing argon and a small amount of mercury vapor. This generates invisible ultraviolet light that excites a fluorescent coating (called phosphor) on the inside of the tube, which then emits visible light.

Statement 2 is incorrect: LED bulbs are much more efficient than CFL bulbs in terms of power consumption and life years.

Statement 3 is correct: LED bulbs consume less power as compared to CFL. LED bulbs are expensive as compared to CFL bulbs. LED bulbs are much more efficient than CFL bulbs.

Explanation

Aspartame is a non-saccharide artificial sweetener approximately 200 times sweeter than sucrose, and is commonly used as a substitute of sugar in foods and beverages. The commercial names for it are NutraSweet, Equal, and Canderel. It is a methyl ester of the aspartic acid / phenylalanine dipeptide. Since Aspartame is several times sweeter than table sugar, hence food items made with small quantities of aspartame yield fewer calories on oxidation.

Explanation

Oilzapper is an eco-friendly technology for oil sludges and oil spills remediation. Oilzapping is the new technique using bacteria to get rid of oil spills. It is a bioremediation technique that involves the use of oil zapping bacteria. In essence, Oilzapper is a concoction of five distinct bacterial strains that have been immobilised and combined with a carrier substance (powdered corn cob). The Oilzapper consumes the hydrocarbon molecules found in crude oil and oily sludge, a dangerous hydrocarbon waste product produced by oil refineries, and transforms them into harmless CO₂ and water. This is exactly what its witty name implies.

Explanation

The blood group of the couple is AB Positive and O Negative. So their biological sons will have either blood group A or B. Thus we can infer that the blood group of the adopted son will be O.