GK (Science)

Hard water contains dissolved salts of calcium (Ca) and magnesium. When water percolates through limestone, chalk, or gypsum deposits, it dissolves calcium and magnesium ions. Hard water is characterized by high mineral content, primarily calcium and magnesium ions.

The rainbow spectrum follows the order ROYGBIV - Red, Orange, Yellow, Green, Blue, Indigo, Violet. Violet is at one extreme end (shortest wavelength, highest frequency) and Red is at the other extreme end (longest wavelength, lowest frequency). Therefore, V & R represents the extreme ends.

Asbestos is a naturally occurring mineral fiber known for its fire-resistant and heat-resistant properties. It has been widely used in construction and insulation materials due to these characteristics. The other options are incorrect - asbestos is not a mobile company, not a specific chemical element, and 'none of these' is incorrect since it is indeed fire-proof.

Tungsten is used as the filament in electric bulbs due to its extremely high melting point (3,422°C) and ability to withstand high temperatures without melting. Iron and copper have much lower melting points and would quickly melt at the temperatures required for incandescent lighting.

Tungsten is used as a filament primarily because it has high electrical resistance, which causes it to heat up and glow when current passes through it. While low resistance is also important for other applications, for a filament to produce light, high resistance is the key property that generates the necessary heat and light emission.

The atomic number of Lithium (Li) is 3, which means it has 3 protons in its nucleus. This places it as the third element in the periodic table, after Hydrogen (1) and Helium (2).

Helium is classified as an inert gas (also known as a noble gas). Noble gases are characterized by having complete valence electron shells, making them extremely stable and unreactive under normal conditions. Tear gas is used for riot control, laughing gas is nitrous oxide (N2O), so these are incorrect.

Germanium (Ge) exhibits properties of both metals and non-metals, placing it in the metalloid category. It has electrical conductivity between that of metals and insulators, making it useful in semiconductors. The correct answer is C because Ge is classified as a metalloid in the periodic table, not a pure metal or non-metal.

An altimeter is specifically designed to measure altitude, which is the height above sea level or ground level. Voltmeter measures voltage, ammeter measures electric current, and barometer measures atmospheric pressure. The correct answer is A because an altimeter is the only instrument among the options that measures altitude.

In the Indian measurement system, 1 quintal equals 100 kilograms. This is a standard conversion used in agriculture and trade. Therefore, 100 kg equals exactly 1 quintal, not 2, 3, or 0.1 quintal.

Marble is primarily composed of calcium carbonate (CaCO₃), which is a chemical compound with a fixed ratio of calcium, carbon, and oxygen atoms. It is not an element (single type of atom), a mixture (variable composition), or an alloy (metal mixture). The correct answer is B because marble has a definite chemical formula.

A calorimeter is the instrument used to measure the amount of heat absorbed or released in a chemical reaction or physical process. Hygrometer measures humidity, megaphone amplifies sound, and neither is used for heat measurement. The correct answer is B because calorimeters are specifically designed for thermal measurements.

Ink is a complex mixture containing dyes, pigments, solvents, and other additives that do not chemically bond in fixed ratios. It cannot be classified as an element (single type of atom) or a compound (fixed chemical formula), and it is certainly not an alloy (metal mixture). The correct answer is A because ink has variable composition.

Dr. P. Venugopal performed India's first successful heart transplant in 1994 at the All India Institute of Medical Sciences (AIIMS), New Delhi. This was a landmark achievement in Indian cardiac surgery. The correct answer is C because Dr. Venugopal is historically recognized for this pioneering medical procedure in India.

Vitamin C is chemically known as ascorbic acid, with the molecular formula C₆H₈O₆. It is an essential nutrient for humans and acts as an antioxidant. Niacin is vitamin B3, and thiamine is vitamin B1. The correct answer is B because ascorbic acid is the specific chemical name for vitamin C.

Freon (chlorofluorocarbon or CFC) is commonly used as a refrigerant in refrigerators and air conditioning systems due to its thermal properties. It undergoes phase changes that absorb and release heat efficiently. Alcohol and acetone are not used as refrigerants in standard refrigeration systems. The correct answer is A because Freon is the traditional refrigerant.

Normal human body temperature is approximately 37°C (or 98.6°F), though it can vary slightly based on individual factors and time of day. Temperatures of 35°C would indicate hypothermia, while 38.5°C or 40°C suggest fever. The correct answer is B because 37°C is the standard average normal body temperature.

Metals contain free electrons (delocalized electrons) that can move freely through the metallic lattice structure. These mobile charge carriers are responsible for conducting electric current. Protons and neutrons remain bound in the atomic nucleus and cannot move to conduct electricity.

Au is the chemical symbol for gold, derived from the Latin word 'aurum'. Chemical symbols are standardized internationally, and each element has a unique one- or two-letter symbol.

Sodium bicarbonate (NaHCO3) is commonly known as baking soda in household use. Washing soda is sodium carbonate (Na2CO3), and hypo is sodium thiosulfate (Na2S2O3).

B is the chemical symbol for boron. Barium has the symbol Ba, and bismuth has the symbol Bi. Chemical symbols are either one or two letters and are derived from the element's English or Latin name.

Iodine is essential for the synthesis of thyroid hormones. Its deficiency leads to inadequate thyroid hormone production, causing the thyroid gland to enlarge (goitre) as it tries to compensate.