Science and Technology: UPSC Previous Year Questions (Prelims)

Explanation

Enzyme-linked immunosorbent assay (ELISA) is a laboratory technique that detects and measures the amount of specific substances in a solution.

Statement 1 is incorrect: The ELISA (Enzyme-Linked Immunosorbent Assay) test is primarily used to detect the presence of antibodies or antigens in the blood, and it is widely employed for diagnosing infections such as HIV, rather than cancer. It is not the first or basic test for cancer detection. Cancer is typically diagnosed using imaging techniques (e.g., MRI, CT scans), biopsies, or specific blood marker tests.

Statement 2 is incorrect: The Rh factor, also known as the Rhesus factor, is a protein that can be present on the surface of red blood cells. Individuals with this protein are classified as Rh-positive (Rh+), while those without it are Rh-negative (Rh-). Globally, the distribution of Rh factor is not evenly split. Approximately 94% of the world’s population is Rh-positive, and only about 6% is Rh-negative. This distribution varies among different populations and regions.

Explanation

In 2005, the Indira Gandhi Centre for Atomic Research (IGCAR) made significant progress in reprocessing the uranium-plutonium mixed carbide fuel used in the Fast Breeder Test Reactor (FBTR). Reprocessing the spent fuel from the FBTR posed significant challenges due to its intense radioactivity and the distinct chemical characteristics of the mixed carbide fuel. The accomplishment of successful reprocessing showcased India’s expertise in managing and recycling this advanced type of nuclear fuel. It also provided critical knowledge for the advancement of next-generation fast breeder reactors, including the Prototype Fast Breeder Reactor (PFBR) at Kalpakkam.

Explanation

Fluorescent tube lights are commonly rated by their color temperature, which is measured in Kelvin (K). Color temperature refers to the hue of light emitted by the tube and it is based on the concept of a black-body radiator.

Option (c) is correct: The color temperature of fluorescent tube lights is typically around 6500 K, which corresponds to "daylight" and provides a bright white light. Options (a), (b) and (d) are incorrect:

Color temperatures as low as 220 K or 273 K are not suitable for lighting as they are far too low. 273 K represents a color temperature lower than a standard incandescent bulb (around 2700 K). A 9000 K light would appear slightly blue and is not commonly used for general room lighting, but rather for specialized purposes like aquarium lighting.

Explanation

Option (c) is correct: Dolby B and Dolby C are noise reduction systems developed by Dolby Laboratories to reduce the background hiss (high-frequency noise) in analog audio recordings, such as cassette tapes. These systems work by compressing and expanding certain frequency ranges during recording and playback to enhance audio clarity. Options (a), (c) and (d) are incorrect:

Frequency Modulated System known as FM is a modulation technique used in radio transmissions, not in tape noise reduction. Amplitude Modulated Systems AM is another modulation technique used in radio, unrelated to Dolby noise reduction. Dolby systems are unrelated to power supply types DC and AC.

Explanation

Statement 1 is incorrect: INSAT-4A was launched on December 5, 2005, using an Ariane 5 rocket from Kourou, French Guiana (not New Mexico).

Statement 2 is correct: Arianespace was responsible for launching INSAT-4A using the Ariane 5 rocket, a major commercial launch vehicle used for heavy payloads like communication satellites.

Statement 3 is correct: Tata Sky, an Indian Direct-to-Home (DTH) service provider, uses the INSAT-4A satellite for providing satellite television services in India.

Explanation

Option (b) is correct: In soldering operations, especially in electronics, the most common solder alloys are made from lead (Pb) and tin (Sn). This combination is used because it has a low melting point, which makes it ideal for joining electronic components without damaging sensitive parts. The typical composition of the solder is 60% tin and 40% lead or 63% tin and 37% lead, though lead-free soldering is becoming more common due to environmental concerns, often comprising tin with small amounts of copper, silver, or other metals. Options (a), (c) and (d) are incorrect:

Iron and tin are not commonly used together in soldering; while iron is typically used as a base metal in some electrical circuit components, it is not a part of the solder itself. Aluminium and lead are not commonly used as soldering materials either. Aluminium is difficult to solder, and its oxide layer makes it less suitable for standard soldering techniques.

Explanation

Option 1 is correct: Benzene was used in the past for dry cleaning but has been largely discontinued due to its toxicity and carcinogenicity.

Option 2 is correct: Carbon tetrachloride was commonly used for dry cleaning in earlier times but has been replaced by safer alternatives due to environmental concerns.

Option 3 is incorrect: Sodium carbonate (washing soda) is not typically used in dry cleaning; it is more commonly used in laundry detergents and cleaning solutions.

Option 4 is correct: Trichloroethylene is widely used as a dry cleaning solvent due to its ability to dissolve oils, greases, and waxes without damaging fabrics.

Explanation

Beach sand minerals are naturally occurring mineral particles found on coastal beaches, often derived from the erosion of rocks and shells. The primary components of beach sand include quartz, a durable and abundant mineral, along with other minerals like feldspar, mica, and ilmenite, as well as heavier minerals such as zircon, rutile, and monazite. The beach sands of many parts of Kerala are known to contain a variety of heavy minerals.

Option 1 is correct: Ilmenite is one of the most abundant minerals in the beach sands of Kerala. It is a source of titanium dioxide, which is used in various industrial applications, including the manufacture of paints and pigments. Odisha is the leading producer of ilmenite, contributing nearly 69% of the total production followed by Kerala and Tamil Nadu.

Option 2 is correct: Zircon is another important mineral found in Kerala’s beach sands. It is used in the production of refractory materials and as a gemstone. Zircon occurs in close association with other heavy minerals such as ilmenite, rutile and monazite in beach sands, along the coastal tracts of the country. Its concentration in the deposits is about 0.6-18.7% of the total heavy minerals. It is found in parts of Gujarat, Maharashtra, Karnataka, Andhra Pradesh, Tamil Nadu, Kerala, Odisha and West Bengal.

Option 3 is correct: Sillimanite is also found in significant amounts in the beach sands. It is an important source of alumina used in the production of aluminum. The resources are located mainly in Odisha, Tamil Nadu, Uttar Pradesh, Andhra Pradesh, Kerala and Assam.

Option 4 is incorrect: Tungsten is not found in the beach sands of Kerala. While it is a valuable mineral, it is not typically associated with the sands in this region. Resources of tungsten-bearing minerals are mainly distributed in Karnataka, Rajasthan, Andhra Pradesh and Maharashtra.

Explanation

Cellulose is a natural polysaccharide and the primary structural component of plant cell walls, providing strength and rigidity. It is widely used in industries for making paper, textiles, and derivatives like cellulose acetate and cellulose nitrate for various applications. Assertion (A) is true: Cellulose acetate, derived from cellulose, is used in the manufacture of shatterproof plastics, including glass used for eyewear and safety applications. These derivatives provide durability and impact resistance, essential for safety applications. Reason (R) is true: Polysaccharides such as cellulose are not soluble in water due to their extensive hydrogen bonding and crystalline structure. This insolubility is a key property of cellulose, which contributes to its stability and strength when used in manufacturing materials like shatterproof glass. Hence, Reason (R) provides the correct explanation of Assertion (A).

Explanation

Statement 1 is incorrect: The common bile duct transports bile from the liver and gallbladder and releases it into the duodenum, not the stomach. Bile aids in the emulsification of fats during digestion. The common bile duct is a vital component of the biliary system. It is formed by the union of the common hepatic duct and the cystic duct and its primary function is to carry bile from the liver and gallbladder.

Statement 2 is correct: The pancreatic duct carries digestive enzymes and bicarbonate from the pancreas into the duodenum. These enzymes play a crucial role in breaking down carbohydrates, proteins, and fats in the small intestine.