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Question 214. Which of the following best explains why the Earth’s magnetic field reverses polarity over geological time? A) The solid inner core stops rotating. B) Changes in the flow patterns of the liquid outer core alter the geodynamo. C) The Sun’s magnetic field forces a reversal. D) Tectonic plate movement drags the magnetic field lines. Answer: B Explanation: Variations in convection currents of molten iron in the outer core cause the geodynamo to change direction, leading to magnetic pole reversals. Question 215. In a chemical reaction, the term “exothermic” means that the reaction: A) Absorbs heat from the surroundings. B) Releases heat to the surroundings. C) Has a positive enthalpy change. D) Requires a catalyst. Answer: B Explanation: Exothermic reactions give off energy, raising the temperature of the surroundings. Question 216. Which of the following best describes the function of the “sodium-chloride (NaCl) crystal lattice” in table salt? A) It conducts electricity in solid form. B) It forms a repeating three-dimensional pattern of alternating Na⁺ and Cl⁻ ions held together by ionic bonds. C. It is a covalent network solid. D) It is composed of metallic bonds.
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Answer: B Explanation: Table salt is an ionic compound with a regular lattice of oppositely charged ions. Question 217. A researcher measures the pH of a solution and obtains a value of 3.2. Which of the following statements is true? A) The solution is basic. B) The solution is neutral. C) The solution is acidic and has a hydrogen ion concentration of about 6.3 × 10⁻⁴ M. D) The solution has a hydrogen ion concentration of 3.2 M. Answer: C Explanation: pH = –log[H⁺]; therefore [H⁺] = 10⁻³·² ≈ 6.3 × 10⁻⁴ M, indicating an acidic solution. Question 218. Which of the following best explains why a planet with a thick atmosphere, such as Venus, has a higher surface temperature than a planet with a thin atmosphere, such as Mars? A) Venus is closer to the Sun. B) The dense CO₂-rich atmosphere on Venus creates a strong greenhouse effect, trapping infrared radiation. C) Mars has a higher albedo. D) Venus rotates faster, generating more heat. Answer: B Explanation: A thick greenhouse gas atmosphere retains solar heat, raising surface temperatures. Question 219. In an experiment to test the effect of catalyst concentration on the rate of a reaction, the independent variable is:
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Explanation: Hardness quantifies resistance to permanent shape change or surface indentation. Question 222. In a closed system, the total mass of reactants and products after a chemical reaction is: A) Greater than before the reaction. B) Less than before the reaction. C) Exactly the same as before the reaction. D. Dependent on temperature. Answer: C Explanation: The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction. Question 223. Which of the following best explains why the speed of sound is slower in air than in water? A) Air is colder than water. B) Air molecules are less densely packed, so the transmission of vibrational energy occurs more slowly. C) Water is heavier than air. D) Sound cannot travel in gases. Answer: B Explanation: Lower density and weaker intermolecular forces in gases reduce the speed of sound. Question 224. The “principle of buoyancy” states that an object immersed in a fluid experiences an upward force equal to: A) The weight of the object.
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B) The weight of the fluid displaced by the object. C) The density of the fluid. D) The pressure at the bottom of the fluid. Answer: B Explanation: Archimedes’ principle: buoyant force equals the weight of the displaced fluid. Question 225. Which of the following best describes the function of “tRNA” during protein synthesis? A) It carries amino acids to the ribosome and matches its anticodon to the mRNA codon. B. It stores genetic information. C) It synthesizes ribosomal RNA. D. It forms the ribosome’s structural core. Answer: A Explanation: Transfer RNA brings specific amino acids and aligns them according to the mRNA codon sequence. Question 226. Which of the following best explains why the Earth’s axial tilt is responsible for the seasons? A. The distance between Earth and Sun changes dramatically over the year. B. The tilt causes different hemispheres to receive varying amounts of solar energy throughout the year. C. The Earth’s orbit becomes elliptical every year. D. The Sun’s brightness fluctuates seasonally. Answer: B
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Answer: B Explanation: A Möbius strip is a one-sided, one-edged surface. Question 230. Which of the following best explains why the Moon shows the same face to Earth? A) The Moon’s rotation period is slower than its orbital period. B) The Moon is tidally locked, meaning its rotational period equals its orbital period around Earth. C) The Earth's gravity pulls the Moon’s far side into darkness. D. The Moon’s atmosphere blocks the view of the far side. Answer: B Explanation: Tidal locking causes the Moon’s rotation to match its orbital period, resulting in one hemisphere always facing Earth. Question 231. Which of the following best describes the “Hertzsprung–Russell diagram” region where stars spend most of their lives? A) Red giant branch B) White dwarf region C) Main sequence D. Supergiant branch Answer: C Explanation: The main sequence is the stable, hydrogen-burning phase where stars spend the majority of their lifetimes. Question 232. In a balanced chemical equation, the coefficient in front of a reactant indicates:
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A) The number of molecules (or moles) of that substance that participate in the reaction. B) The temperature required for the reaction. C) The amount of energy released. D. The speed of the reaction. Answer: A Explanation: Coefficients balance the number of atoms of each element on both sides of the equation. Question 233. Which of the following best describes the “law of independent assortment”? A) Genes located on the same chromosome always segregate together. B. Alleles of different genes are distributed into gametes independently of one another, assuming the genes are on different chromosomes or far apart. C. All traits are inherited together. D. Only dominant alleles are assorted independently. Answer: B Explanation: Mendel’s second law states that alleles for different traits assort independently during meiosis when not linked. Question 234. Which of the following best explains the term “biomass” in an ecosystem? A) The total number of individuals. B. The total mass of living (or recently dead) organic material in a given area. C) The amount of sunlight received. D) The diversity of species present. Answer: B
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B) The inner core is constantly cooled by the mantle. C) The core is composed of a different element that never melts. D. Magnetic forces keep it solid. Answer: A Explanation: Extreme pressure in the inner core increases the melting point of iron, keeping it solid despite high temperature. Question 238. Which of the following best describes the “principle of least action” as used in optics? A. Light travels the shortest distance. B) Light follows the path that requires the least time, which can involve refraction when moving between media of different speeds. C) Light always moves at a constant speed independent of medium. D) Light’s wavelength determines its speed. Answer: B Explanation: Fermat’s principle states that light takes the path of minimal travel time, explaining refraction. Question 239. In the carbon cycle, which process removes CO₂ from the atmosphere and stores it in long-term geological reservoirs? A) Photosynthesis B) Combustion C) Weathering of silicate rocks that form carbonate minerals D) Respiration Answer: C Explanation: Chemical weathering of silicate rocks consumes atmospheric CO₂, forming stable carbonate rocks.
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Question 240. Which of the following best explains why a “bungee jumper” experiences a greater force when the cord is stretched beyond its elastic limit? A) The cord’s material becomes a superconductor. B) The cord behaves like a spring with a higher effective spring constant after yielding, increasing the restoring force. C) The jumper’s mass increases. D) Air resistance becomes negligible. Answer: B Explanation: Once the elastic limit is exceeded, the material’s stiffness increases, producing a larger restoring force. Question 241. Which of the following best describes the “principle of superposition” as it applies to quantum states? A) A particle can exist in multiple mutually exclusive states simultaneously until measured. B. Particles can only be in one state at a time. C) Quantum states cannot interfere. D) Superposition only applies to photons. Answer: A Explanation: Quantum superposition allows a system to be in a combination of states until observation collapses it to a single outcome. Question 242. In a closed ecosystem, which of the following is the primary source of nitrogen for plant growth? A) Atmospheric N₂ directly absorbed by roots. B) Nitrate (NO₃⁻) produced by nitrogen-fixing bacteria and made available through the soil.
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Question 245. In a chemical reaction, the “rate law” expresses the relationship between: A. The equilibrium constant and temperature. B. The reaction rate and the concentrations of reactants (and possibly catalysts). C. The activation energy and the enthalpy change. D. The mass of reactants and products. Answer: B Explanation: The rate law quantifies how the speed of a reaction depends on reactant concentrations and other factors. Question 246. Which of the following best describes the “principle of conservation of momentum” in a closed system? A) Momentum can increase if kinetic energy increases. B) The total vector sum of momenta of all objects remains constant unless acted upon by external forces. C) Momentum is always zero. D) Momentum is conserved only in elastic collisions. Answer: B Explanation: In the absence of external forces, total momentum is conserved, regardless of the type of collision. Question 247. Which of the following best explains why a “heat engine” cannot be 100 % efficient? A) Friction always dissipates energy. B) The second law of thermodynamics requires that some heat be expelled to a colder reservoir; not all heat can be converted to work.
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C. Energy is lost as sound. D) Engines always leak fuel. Answer: B Explanation: The second law imposes a fundamental limit on conversion efficiency; a portion of heat must be rejected. Question 248. In a population genetics context, “genetic drift” is most pronounced in: A) Very large populations. B) Small, isolated populations where random sampling effects can change allele frequencies dramatically. C) Populations with high mutation rates only. D. Populations under strong natural selection only. Answer: B Explanation: Random fluctuations have a larger impact when the gene pool is small. Question 249. Which of the following best describes the “principle of least time” as it applies to the refraction of light entering water from air? A) Light bends toward the normal because it travels faster in water. B) Light bends away from the normal because it travels slower in water, taking the path that minimizes travel time. C. Light does not change direction. D. Light speeds up in water, causing no refraction. Answer: B Explanation: Light slows in water, so it bends toward the normal to minimize overall travel time, as described by Snell’s law derived from Fermat’s principle.
