63rd Prelims 2018

Explanation:

Quartz crystals used in clocks are primarily composed of silicon dioxide (SiO2). This compound exhibits piezoelectric properties, generating an electric charge when subjected to mechanical pressure or vibration, making it ideal for precise timekeeping. Sodium silicate, Germanium Oxide, and Titanium Dioxide serve different industrial purposes such as adhesives, optical devices, and pigments, respectively.

Explanation:

Bromine is a red-brown liquid at room temperature and is a halogen element (Br, atomic number 35). It is used in flame retardants, pharmaceuticals, dyes, and water disinfectants. Unlike chlorine (gas) or iodine (solid), bromine naturally exists as a liquid under standard conditions.

Explanation:

Oxygen and acetylene are commonly used in oxy-acetylene welding. Oxygen supports combustion, producing a high-temperature flame when combined with acetylene, which serves as the fuel. This combination is ideal for welding and cutting metals. Hydrogen and nitrogen are not used in standard welding processes.

Explanation:

Galvanized iron pipes are coated with zinc to prevent corrosion. Zinc acts as a sacrificial layer, corroding before the iron underneath, thereby extending the pipe's lifespan. Mercury, lead, and chromium are not used for standard galvanization purposes.

Explanation:

The visible spectrum spans approximately 3900 to 7600 Angstroms (390–700 nm), representing the colors violet through red. Wavelengths shorter than 3900 Angstrom belong to ultraviolet, while those longer than 7600 Angstrom belong to the infrared region.

Explanation:

Detergents for laundry are mostly sulfonates, specifically alkyl benzene sulfonates (ABS). These surfactants lower water's surface tension, remove grease and dirt effectively, and are compatible with hard and soft water. Carbonates and bicarbonates are mild cleaning agents, while bismuthates are not used in detergents.

Explanation:

Human sweat contains multiple elements, including sulphur, magnesium, iron, zinc, sodium, potassium, calcium, and trace metals. The excretion varies depending on diet, hydration, and physical activity. Therefore, it is 'more than one of the above'.

Explanation:

Blue vitriol refers to copper sulphate (CuSO4·5H2O), a blue crystalline compound used as a fungicide, herbicide, and laboratory reagent. Nickel sulphate, sodium sulphate, and iron sulphate are distinct compounds with different industrial applications.

Explanation:

The nucleus is the central region of an atom containing protons (positive charge) and neutrons (neutral). Electrons orbit around the nucleus. The number of protons defines the element.

Explanation:

Sublimation is the process in which a solid changes directly into a gas without passing through the liquid phase, e.g., dry ice or naphthalene. Condensation, evaporation, and boiling involve liquid-gas transitions.

Explanation:

Insulin, secreted by the pancreas, regulates carbohydrate metabolism. It promotes glucose uptake and glycogen formation while inhibiting gluconeogenesis. It indirectly affects fat and protein metabolism but primarily controls carbohydrates.

Explanation:

Rice is predominantly composed of carbohydrates (starch), making it a high-energy staple food. Wheat, barley, and maize contain carbohydrates but also proteins and fats; hence, they are not primarily carbohydrate-based.

Explanation:

Platinum is denser and heavier than gold, silver, and mercury. It is a transition metal valued for corrosion resistance, rarity, and industrial applications like catalytic converters and jewelry.

Explanation:

Both Penicillin and Sulfadiazine are antibiotics. Aspirin and Paracetamol are not antibiotics; they are used for pain relief and fever reduction. The correct choice should reflect 'more than one of the above' since multiple options are antibiotics.

Explanation:

Stainless steel is primarily composed of iron and chromium, with possible additions of nickel, molybdenum, and carbon. Chromium forms a protective oxide layer to prevent corrosion. Nickel and zinc are present in some alloys but are not the main components.

Explanation:

Plaster of Paris is derived from gypsum (calcium sulfate dihydrate). When heated, gypsum loses water molecules to form a powder, which sets into a hard solid when mixed with water. It is widely used for immobilizing broken bones and in construction.

Explanation:

Alkenes are unsaturated hydrocarbons containing at least one carbon-carbon double bond (general formula CnH2n). Alkanes have single bonds, alkynes have triple bonds, and ionic bond is not a hydrocarbon.

Explanation:

Vinegar is a dilute solution (5–8%) of acetic acid (CH3COOH) in water. Methanol and ethanol are alcohols, while ethyl acetate is an ester used as a solvent and flavoring agent.

Explanation:

Car batteries (lead-acid batteries) use sulfuric acid (H2SO4) as the electrolyte. It reacts with lead plates to generate electrical energy. Acetic, hydrochloric, and nitric acids are not used in standard car batteries.

Explanation:

Soda water is carbonated, containing dissolved carbon dioxide (CO2). When the bottle is opened, the pressure drops, causing CO2 to escape as bubbles, producing the fizzy effect. Hydrogen, nitrogen, and sulphur dioxide are not present in significant amounts.