Science and Technology: UPSC Previous Year Questions (Prelims)

Explanation

Fluorine is the most reactive halogen because:

Small Atomic Size: Fluorine has the smallest atomic radius among halogens, leading to a strong attraction for electrons. High Electronegativity: It is the most electronegative element in the periodic table, making it highly effective in gaining electrons. Low Bond Dissociation Energy: The F-F bond in molecular fluorine is weak due to electron repulsion between the two small atoms, which makes it highly reactive. Reactivity Trend in Halogens:

Fluorine > Chlorine > Bromine > Iodine

Explanation

The distinctive pungent odour of garlic is due to sulphur-containing compounds, mainly allicin. These compounds are formed when alliin is converted by the enzyme alliinase during chopping or crushing.

Explanation

Eugenol is the active component in clove oil, contributing to its distinct aroma and analgesic properties. It is widely used in dental care and as a natural preservative.

Explanation

Mustard gas (sulfur mustard) was widely used as a chemical weapon during World War I. It causes blistering of the skin and mucous membranes, along with severe respiratory damage.

Explanation

Option (a) is correct: Hydrogen has the highest calorific value of around 120-150 MJ/kg, making it an efficient and eco-friendly fuel. Combustion of hydrogen produces only water, contributing to clean energy initiatives. Options (b), (c) and (d) are incorrect:

Charcoal: Has a calorific value of 30 MJ/kg(approx.), significantly lower than hydrogen. Natural gas: Primarily composed of Methane, With a fuel value of around 55 MJ/kg(approx.), it is lower than hydrogen but widely used due to availability. Gasoline: Though energy-dense around 47 MJ/kg (approx.), but lower than hydrogen.

Explanation

Option (d) is correct: Ethylene glycol is a widely used anti-freeze for automobile engines. It effectively lowers the freezing point of the coolant, preventing it from freezing in cold climates. Additionally, it raises the boiling point of the coolant, ensuring efficient heat transfer during engine operation. Options (a), (b) and (c) are incorrect:

Propyl alcohol is rarely used as an anti-freeze due to its lower efficiency and higher cost compared to ethylene glycol. While ethanol has some anti-freeze properties, it is volatile and less efficient than ethylene glycol. Although methanol can be used as an anti-freeze, it is highly toxic and less efficient compared to ethylene glycol.

Explanation

The pituitary gland, often termed the "master gland,” regulates various endocrine glands through its tropic hormones. The parathyroid gland regulates calcium and phosphate balance in the body via parathyroid hormone (PTH) and its activity is independent of pituitary gland control. It is self-regulating, depending directly on calcium levels in the blood. Options (a), (b), and (c) are incorrect: The thyroid, gonads, and adrenal glands are regulated by pituitary tropic hormones such as TSH (thyroid-stimulating hormone), LH/FSH (for gonads), and ACTH (adrenocorticotropic hormone) for the adrenal glands. These glands depend on the pituitary to regulate the production of key hormones that control metabolism, growth, and stress responses.

Explanation

Oxygen transportation in the human body is essential for cellular respiration, which generates energy in the form of ATPs. This process ensures oxygen is delivered to tissues and carbon dioxide is removed efficiently. Oxygen enters the body through the lungs (2), binds to hemoglobin in the blood (1), and is transported to the tissues (3) where it is utilized for energy production. This sequence reflects the physiological process of oxygen transport.

Explanation

Option (b) is correct: The corpus luteum is a temporary endocrine structure found in the ovary formed after ovulation. It produces progesterone, which is critical for maintaining the uterine lining and supporting pregnancy in the early stages. Options (a), (c), and (d) are incorrect: The corpus luteum is specific to the ovary and is unrelated to the brain, pancreas, or spleen.

Explanation

Alpha-keratin is a fibrous structural protein that forms the primary component of the skin, hair, nails, horns, and hooves in mammals. It belongs to the keratin family of proteins and is rich in disulfide bonds, which provide strength, durability, and elasticity to epithelial cells. In the skin, alpha-keratin creates a protective barrier against physical damage, dehydration, and pathogens. In hair and nails, it contributes to their hardness and resistance to wear. Options (a), (c), and (d) are incorrect: Alpha-keratin is not found in blood, lymph, or eggs. These tissues have other proteins like hemoglobin (in blood) or albumin (in eggs).