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PAU General Sciences (Castilla y León) study materials
PAU General Sciences (Castilla y León) study resources

PAU General Sciences (Castilla y León) practice questions

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Question 1Ciencias Generales

What is the initial step of the scientific method when conducting an empirical investigation in General Sciences?

  1. Formulating a mathematical law before collecting data
  2. Making systematic observations and posing a testable research question Correct answer.
  3. Drawing definitive conclusions prior to experimental verification
  4. Publishing preliminary hypotheses in scientific journals

Explanation

The scientific method begins with careful, objective observation of a natural phenomenon, which leads to formulating a clear, testable research question. Subsequent steps include hypothesis generation, experimental testing, data collection, and evidence-based conclusion.

Question 2Ciencias Generales

In a controlled scientific experiment evaluating plant growth under varying light wavelengths, what represents the independent variable?

  1. The light wavelength intentionally manipulated by the researcher Correct answer.
  2. The height and biomass of the plants measured after four weeks
  3. The ambient room temperature and soil moisture kept constant
  4. The systematic error introduced by measurement instruments

Explanation

The independent variable is the single factor intentionally changed or manipulated by the experimenter (in this case, light wavelength). The dependent variable is measured to observe the response caused by altering the independent variable.

Question 3Ciencias Generales

Why is a negative control group essential when testing the efficacy of a new chemical water purifier?

  1. To ensure the independent variable is maximized in every test tube
  2. To establish a baseline measurement in the absence of the active purifying agent Correct answer.
  3. To guarantee that all experimental samples produce identical quantitative results
  4. To eliminate the need for repeating experimental trials

Explanation

A negative control group receives no active treatment, providing a baseline to confirm that observed changes in experimental groups are genuinely caused by the purifying agent rather than background environmental factors.

Question 4Ciencias Generales

Which characteristic is essential for a scientific hypothesis to be valid within the framework of modern science?

  1. It must be proven true beyond all future doubt prior to testing
  2. It must be testable and capable of being proven false (falsifiable) Correct answer.
  3. It must rely exclusively on qualitative personal opinions
  4. It must align with popular public voting consensus

Explanation

Karl Popper demonstrated that scientific hypotheses must be falsifiable-meaning there must be conceivable empirical observations or experimental outcomes that could prove the hypothesis false. Hypotheses that cannot be tested or falsified fall outside scientific inquiry.

Question 5Ciencias Generales

A laboratory balance consistently measures a 10.00 gram standard mass as 10.45 grams across twenty consecutive trials. How should this measurement error be classified?

  1. Random error affecting precision
  2. Systematic error affecting accuracy Correct answer.
  3. Statistical variance caused by sample size limits
  4. Human transcription error

Explanation

Systematic error causes measurements to consistently deviate from the true value in the same direction (offset bias), impairing accuracy despite high repeatability (precision). Recalibrating the balance eliminates systematic error.

Question 6Ciencias Generales

Which graphical representation is most suitable for displaying continuous data showing river nitrate concentration over a twelve-month period?

  1. Pie chart
  2. Line graph Correct answer.
  3. Bar chart
  4. Venn diagram

Explanation

A line graph is ideal for continuous numerical data plotted against a continuous independent variable such as time, clearly revealing trends, seasonal fluctuations, and rates of change over consecutive months.

Question 7Ciencias Generales

Why does increasing sample size from 10 to 1,000 subjects improve the statistical reliability of a clinical trial?

  1. It completely eliminates all systematic measurement errors
  2. It reduces the margin of random error and increases statistical power Correct answer.
  3. It converts qualitative observational data into physical constants
  4. It guarantees that every subject experiences an identical therapeutic outcome

Explanation

Larger sample sizes reduce random sampling variation, narrow confidence intervals, and increase statistical power, making the study sample more representative of the target population.

Question 8Ciencias Generales

An epidemiological study observes a strong positive correlation between ice cream consumption and sunburn cases in coastal towns. What logical fallacy occurs if one concludes that eating ice cream causes sunburn?

  1. Confusing correlation with causation due to an unmeasured confounding variable (ambient summer temperature) Correct answer.
  2. Ignoring the law of conservation of mass in biological tissue
  3. Assuming random measurement error accounts for all observed data
  4. Failing to establish a double-blind peer review board

Explanation

Correlation indicates two variables fluctuate together, but does not prove direct causation. Hot summer weather acts as a confounding variable that independently increases both ice cream sales and outdoor sun exposure.

Question 9Ciencias Generales

In scientific hypothesis testing, what does a p-value of less than 0.05 (p < 0.05) signify?

  1. There is a 95% probability that the null hypothesis is entirely true
  2. The probability of observing the experimental results by random chance under the null hypothesis is less than 5% Correct answer.
  3. The experimental sample size was 5% smaller than required
  4. The experiment contains a 5% systematic calibration error

Explanation

A p-value < 0.05 indicates that if the null hypothesis were true (no real effect), there would be less than a 5% chance of obtaining results as extreme as observed. This justifies rejecting the null hypothesis in favor of statistical significance.

Question 10Ciencias Generales

Two sets of soil pH measurements yield the following results: Group A = {6.8, 6.9, 6.8, 6.9} and Group B = {5.5, 6.8, 7.2, 8.1}. How do their standard deviations compare?

  1. Group A has a lower standard deviation than Group B, indicating greater precision Correct answer.
  2. Group B has a lower standard deviation than Group A, indicating greater accuracy
  3. Both groups have identical standard deviations because their means are similar
  4. Group A has a higher standard deviation because its values are closer together

Explanation

Standard deviation measures data dispersion around the mean. Group A values are tightly clustered (SD ≈ 0.06), reflecting high precision, whereas Group B values are widely spread (SD ≈ 1.07).

Question 11Ciencias Generales

What is the primary advantage of a double-blind experimental design in clinical health trials?

  1. It prevents both participant expectations and researcher assessment bias from influencing results Correct answer.
  2. It eliminates the need to obtain informed consent from participants
  3. It doubles the rate at which experimental drugs are metabolized
  4. It guarantees 100% efficacy for all tested pharmaceutical compounds

Explanation

In a double-blind trial, neither the subjects nor the evaluating researchers know who receives the active drug versus placebo. This prevents observer bias, subjective scoring distortion, and placebo expectations.

Question 12Ciencias Generales

Which indicator strongly suggests that a published claim belongs to pseudoscience rather than rigorous science?

  1. Reliance on anecdotal testimonials while ignoring peer-reviewed empirical counterevidence Correct answer.
  2. Open publication of raw experimental data and methodology for independent replication
  3. Continuous modification of theoretical concepts upon discovering new contradictory facts
  4. Use of quantitative error analysis and statistical hypothesis testing

Explanation

Pseudoscience relies heavily on subjective anecdotes, unfalsifiable claims, and selective cherry-picking of favorable stories, while refusing to engage with rigorous empirical testing or peer-reviewed counterevidence.

Question 13Ciencias Generales

What role does independent peer review play in academic scientific publishing?

  1. It permits commercial sponsors to alter experimental outcomes prior to release
  2. It subjects submitted manuscripts to critical evaluation by independent subject experts before publication Correct answer.
  3. It automatically converts scientific theories into unalterable physical laws
  4. It eliminates the necessity of repeating laboratory experiments

Explanation

Peer review involves independent experts assessing research manuscripts for methodological rigor, logical consistency, statistical validity, and originality before publication in scholarly journals.

Question 14Ciencias Generales

A bacterial population doubles every 30 minutes in an unconstrained nutrient medium. Which mathematical model describes this growth pattern?

  1. Linear growth model
  2. Exponential growth model Correct answer.
  3. Sinusoidal wave model
  4. Inverse square model

Explanation

Exponential growth occurs when the rate of population change is directly proportional to the current population size ($N(t) = N_0 \cdot 2^{t/t_d}$), producing an accelerating growth curve under unlimited resource conditions.

Question 15Ciencias Generales

Which principle forms the core foundation of bioethics in clinical research according to the Declaration of Helsinki?

  1. Commercial profitability must take precedence over subject safety
  2. Voluntary informed consent and protection of subject welfare are paramount Correct answer.
  3. Researchers may bypass ethical approval if sample sizes exceed 10,000
  4. Experimental risks can be concealed from subjects to maintain double-blinding

Explanation

Bioethical frameworks dictate that human subject safety, well-being, rights, and informed voluntary consent take absolute priority over scientific curiosity or commercial interests.

Question 16Ciencias Generales

Why are systematic reviews and meta-analyses considered the highest level of evidence in the hierarchy of clinical research?

  1. They combine quantitative data from multiple independent studies to increase statistical power and mitigate single-study bias Correct answer.
  2. They replace empirical laboratory testing with theoretical computer simulations
  3. They rely exclusively on qualitative opinions expressed by senior department heads
  4. They eliminate the need for confidence intervals in reporting results

Explanation

Meta-analyses aggregate data across numerous independent randomized controlled trials, reducing random error and study-specific biases to provide a robust summary estimate of treatment efficacy.

Question 17Ciencias Generales

A diagnostic blood test has 98% sensitivity and 90% specificity. If tested on a population with very low disease prevalence (0.1%), what occurs regarding the test's positive predictive value (PPV)?

  1. PPV approaches 100% because sensitivity is high
  2. PPV drops significantly, yielding more false positives than true positives overall Correct answer.
  3. PPV remains identical to sensitivity regardless of population prevalence
  4. PPV equals specificity divided by sensitivity

Explanation

When disease prevalence is extremely low, the total number of false positives generated from the 10% non-specific uninfected group far exceeds the few true positives detected from the 0.1% infected group, resulting in a low PPV (Bayes' Theorem).

Question 18Ciencias Generales

What is publication bias (the 'file-drawer effect') in scientific literature?

  1. The tendency for journals to publish studies with statistically significant positive results more readily than studies with null or negative findings Correct answer.
  2. The illegal duplication of copyright-protected scientific articles across public repositories
  3. The automated deletion of old research paper PDFs after ten years of publication
  4. The preferential citation of articles published exclusively in local languages

Explanation

Publication bias occurs when studies showing statistically significant positive effects are published, while studies finding no effect remain unpublished in 'file drawers'. This distorts literature reviews and overestimates intervention efficacy.

Question 19Ciencias Generales

What is the primary function of an Institutional Review Board (IRB) or Clinical Ethics Committee in research institutions?

  1. To audit financial tax returns filed by academic principal investigators
  2. To review research protocols independently to ensure protection of human participants' safety and rights Correct answer.
  3. To negotiate intellectual property patent licensing agreements with commercial corporations
  4. To manage digital server infrastructure for institutional websites

Explanation

IRBs are independent ethics committees tasked with evaluating research proposals involving human subjects to confirm that risks are minimized, informed consent is obtained, and ethical guidelines are strictly enforced.

Question 20Ciencias Generales

When calculating rectangle area ($A = L \cdot W$), if length $L = 10.0 \pm 0.2\text{ m}$ (2% error) and width $W = 5.0 \pm 0.1\text{ m}$ (2% error), what is the calculated area and its propagated relative uncertainty?

  1. Area = 50.0 m² with relative uncertainty of 4% (50.0 ± 2.0 m²) Correct answer.
  2. Area = 50.0 m² with relative uncertainty of 0.2% (50.0 ± 0.1 m²)
  3. Area = 15.0 m² with relative uncertainty of 2% (15.0 ± 0.3 m²)
  4. Area = 50.0 m² with absolute uncertainty of 0.3 m²

Explanation

For multiplication of independent measurements ($A = L \cdot W$), percentage relative uncertainties add directly: \% \sigma_A = \% \sigma_L + \% \sigma_W = 2\% + 2\% = 4\%. Calculated area = 50.0 m², so absolute uncertainty = 50.0 \cdot 0.04 = 2.0\text{ m}^2.

Question 21Ciencias Generales

Which physical law states that energy can neither be created nor destroyed, only transformed from one form to another?

  1. First Law of Thermodynamics (Law of Conservation of Energy) Correct answer.
  2. Second Law of Thermodynamics (Law of Increasing Entropy)
  3. Third Law of Thermodynamics (Absolute Zero limit)
  4. Hubble's Law of Cosmic Expansion

Explanation

The First Law of Thermodynamics establishes that total energy in an isolated system remains constant over time; energy converts between chemical, thermal, electrical, and kinetic forms without net creation or loss.

Question 22Ciencias Generales

Which resource is classified as a non-renewable energy source?

  1. Anthracite Coal Correct answer.
  2. Photovoltaic Solar Radiation
  3. Wind Kinetic Energy
  4. Geothermal Surface Steam

Explanation

Coal is a fossil fuel formed over millions of years from buried organic plant matter. Because its consumption rate vastly exceeds its geological formation rate, it is finite and non-renewable.

Question 23Ciencias Generales

How do solar photovoltaic panels generate electric current from incident sunlight?

  1. By absorbing photons to excite valence electrons across semiconductor p-n junctions (photovoltaic effect) Correct answer.
  2. By boiling water into high-pressure steam to spin mechanical turbines
  3. By splitting water molecules into hydrogen gas for direct combustion
  4. By capturing radio wave frequencies to charge electromagnetic coils

Explanation

Photovoltaic cells use semiconductor materials (such as silicon p-n junctions) where absorbed solar photons transfer energy to electrons, creating electron-hole pairs that flow as direct electric current.

Question 24Ciencias Generales

Why do greenhouse gases (GHGs) like carbon dioxide and methane contribute to Earth's atmospheric warming?

  1. They absorb outgoing longwave infrared radiation re-emitted by Earth's surface and re-radiate thermal energy Correct answer.
  2. They absorb incoming shortwave ultraviolet solar light before it reaches the ground
  3. They generate thermal heat internally through radioactive decay of carbon isotopes
  4. They block atmospheric ozone from reflecting cosmic rays back into deep space

Explanation

Earth absorbs shortwave solar radiation and re-emits longwave thermal infrared radiation. Greenhouse gas molecules absorb this outgoing infrared radiation via vibrational quantum transitions and re-emit heat back toward the troposphere.

Question 25Ciencias Generales

How many Joules of energy are equivalent to one kilowatt-hour (1 kWh)?

  1. 3.6 × 10⁶ Joules (3,600,000 J) Correct answer.
  2. 1.0 × 10³ Joules (1,000 J)
  3. 6.0 × 10⁴ Joules (60,000 J)
  4. 3.6 × 10³ Joules (3,600 J)

Explanation

Power is energy per unit time ($1\text{ W} = 1\text{ J/s}$). Therefore, $1\text{ kWh} = 1,000\text{ W} \cdot 3,600\text{ s} = 3.6 \times 10^6\text{ Joules}$ (or 3.6 Megajoules).

Question 26Ciencias Generales

What does a product's 'carbon footprint' measure?

  1. The total amount of greenhouse gases emitted across its lifecycle, expressed in CO₂ equivalents (CO₂e) Correct answer.
  2. The mass percentage of elemental carbon contained in the product's physical structure
  3. The surface area of land required to mine the raw materials for production
  4. The concentration of soot particulate matter released during product combustion

Explanation

A carbon footprint quantifies the cumulative direct and indirect emissions of carbon dioxide and other greenhouse gases (methane, N₂O) generated during raw material extraction, manufacturing, transport, use, and disposal, normalized as CO₂ equivalents.

Question 27Ciencias Generales

According to the Second Law of Thermodynamics, why can no heat engine convert thermal energy into mechanical work with 100% efficiency?

  1. Because part of the heat energy must inevitably be rejected to a lower-temperature cold sink, increasing entropy Correct answer.
  2. Because friction between mechanical gears permanently destroys energy atoms
  3. Because gravitational potential energy counteracts thermal expansion in closed systems
  4. Because thermal energy moves spontaneously from cold objects to hotter objects

Explanation

The Second Law (Kelvin-Planck statement) proves that operating heat engines must transfer heat from a hot reservoir to a cold sink, dissipating unusable waste heat and increasing universe entropy (\Delta S > 0), preventing 100% thermal efficiency.

Question 28Ciencias Generales

In a hydroelectric plant (such as Aldeadávila Dam in Castilla y León), what energy conversions occur during electricity generation?

  1. Gravitational potential energy → Kinetic energy of water → Rotational mechanical energy of turbines → Electrical energy Correct answer.
  2. Nuclear binding energy → Chemical potential energy → Thermal energy → Direct electrical current
  3. Radiant solar energy → Chemical biomass energy → Elastic potential energy → Electrical current
  4. Thermal expansion energy → Electromagnetic radiation → Kinetic energy → High voltage direct current

Explanation

Water stored behind a dam possesses gravitational potential energy ($E_p = mgh$). As it flows through penstocks, potential energy converts to kinetic energy, driving turbine rotation, which spins electromagnetic generators to produce electrical power.

Question 29Ciencias Generales

The power available in a wind turbine airstream is given by $P = \frac{1}{2} \rho A v^3$. If wind speed $v$ doubles, how does the available wind power change?

  1. It increases by a factor of 8 (2³ = 8) Correct answer.
  2. It doubles (increases by a factor of 2)
  3. It quadruples (increases by a factor of 4)
  4. It increases by a factor of 16

Explanation

Available kinetic power in wind scales cubically with velocity ($P \propto v^3$). If wind velocity doubles ($2v$), available power increases by $2^3 = 8$ times, highlighting why turbine siting in high-wind regions is crucial.

Question 30Ciencias Generales

How does nuclear fission differ fundamentally from nuclear fusion?

  1. Fission splits a heavy atomic nucleus into lighter fragments, whereas fusion combines light nuclei into a heavier nucleus Correct answer.
  2. Fission combines hydrogen isotopes, whereas fusion splits uranium-235 atoms
  3. Fission produces zero radioactive waste, whereas fusion generates large volumes of high-level waste
  4. Fission requires temperatures exceeding 100 million Kelvin, whereas fusion occurs spontaneously at room temperature

Explanation

Nuclear fission splits heavy actinide nuclei (e.g., Uranium-235) releasing energy and neutrons, while fusion joins light atomic nuclei (e.g., Deuterium and Tritium) to form Helium at extreme plasma temperatures.

Question 31Ciencias Generales

Biomass energy systems generate heat or electricity by combusting agricultural residues. Why can biomass be considered carbon-neutral under sustainable forestry practices?

  1. The CO₂ released during combustion equals the CO₂ absorbed by plants during growth via photosynthesis Correct answer.
  2. Biomass combustion emits oxygen gas instead of greenhouse carbon compounds
  3. Combustors trap all carbon atoms permanently inside ash mineral residues
  4. Biomass fuel contains no chemical carbon bonds prior to ignition

Explanation

Biomass recycling operates within the short-term biological carbon cycle: carbon dioxide emitted during combustion matches the atmospheric CO₂ fixed by plants during recent photosynthesis, yielding zero net atmospheric addition if replanted sustainably.

Question 32Ciencias Generales

What is the maximum theoretical efficiency (\eta_{max}) of a heat engine operating between a hot reservoir at 500 K and a cold environment at 300 K?

  1. 40% (\eta = 1 - 300/500 = 0.40) Correct answer.
  2. 60% (\eta = 300/500 = 0.60)
  3. 20% (\eta = (500-300)/1000 = 0.20)
  4. 100% (\eta = 1.00)

Explanation

Carnot efficiency sets the upper thermodynamic limit for heat engines: \eta_{max} = 1 - \frac{T_C}{T_H} = 1 - \frac{300}{500} = 1 - 0.60 = 0.40 or 40%.

Question 33Ciencias Generales

Why is methane (CH₄) considered a potent greenhouse gas compared to carbon dioxide (CO₂) despite its lower atmospheric concentration?

  1. Methane has a much higher Global Warming Potential (GWP ≈ 28–36 over 100 years) due to higher infrared absorption efficiency Correct answer.
  2. Methane remains permanently in the atmosphere for thousands of years without degrading
  3. Methane reacts with nitrogen to form stratospheric nitric acid rain
  4. Methane reflects visible sunlight directly onto polar ice sheets

Explanation

Methane absorbs infrared radiation much more effectively per molecule than CO₂, giving it a 100-year Global Warming Potential (GWP) roughly 28–36 times greater than CO₂ despite its shorter atmospheric lifespan (~12 years).

Question 34Ciencias Generales

How does increased atmospheric CO₂ lead to ocean acidification, impacting marine organisms with calcium carbonate shells?

  1. Dissolved CO₂ forms carbonic acid (H₂CO₃), increasing H⁺ ions which react with carbonate ions (CO₃²⁻), reducing shell calcification Correct answer.
  2. Dissolved CO₂ neutralizes ocean salt, raising pH above 12.0 and dissolving organic tissues
  3. CO₂ gas bubbles physically erode coral reefs through mechanical friction
  4. Atmospheric CO₂ strips dissolved oxygen from ocean water, preventing cellular respiration

Explanation

CO₂ dissolves in seawater to form carbonic acid (\text{CO}_2 + \text{H}_2\text{O} \rightleftharpoons \text{H}_2\text{CO}_3 \rightleftharpoons \text{H}^+ + \text{HCO}_3^-). Free H⁺ ions lower ocean pH and combine with carbonate ions (\text{CO}_3^{2-}), depleting the carbonate required by corals and mollusks to build \text{CaCO}_3 shells.

Question 35Ciencias Generales

What is the primary operational role of pumped-storage hydroelectric stations in grid-scale energy management?

  1. Storing excess electrical energy during off-peak hours by pumping water uphill, then generating power during peak demand Correct answer.
  2. Purifying agricultural runoff water using reverse osmosis membrane filters
  3. Converting grid electricity directly into natural gas for residential pipelines
  4. Eliminating the need for electrical transmission lines

Explanation

Pumped-storage hydro acts as a giant gravitational battery: low-cost surplus electricity (e.g. solar/wind) pumps water from a lower reservoir to an upper reservoir; during peak demand, released water flows down through turbines to generate power.

Question 36Ciencias Generales

Which strategy represents a key component of national decarbonization pathways aimed at achieving net-zero greenhouse gas emissions?

  1. Electrifying heating and transport sectors while expanding zero-emission renewable energy generation Correct answer.
  2. Replacing all solar panels with heavy oil power generation units
  3. Decreasing building energy efficiency standards to lower construction costs
  4. Increasing coal subsidies to accelerate urban industrialization

Explanation

Decarbonization relies on electrifying end-use sectors (electric vehicles, heat pumps) while simultaneously transitioning grid power generation to zero-carbon sources (wind, solar, hydro, nuclear).

Question 37Ciencias Generales

In thermodynamic analysis, how does exergy differ fundamentally from energy?

  1. Exergy represents the maximum useful work obtainable from a system as it comes to equilibrium with its environment, whereas energy is strictly conserved Correct answer.
  2. Exergy is a non-quantifiable subjective property, whereas energy has fixed units
  3. Exergy is conserved in all real processes, whereas energy decreases during friction
  4. Exergy applies only to electromagnetic waves, whereas energy applies to mechanical solids

Explanation

Energy is conserved under the First Law, but exergy (the quality or work potential of energy relative to reference environment conditions) is destroyed (\text{Ex}_{destroyed} = T_0 S_{gen}) by irreversible processes like friction and heat transfer across finite temperature differences.

Question 38Ciencias Generales

Which climate feedback mechanism acts as a positive (amplifying) feedback loop in global warming dynamics?

  1. Melting Arctic sea ice reduces planetary albedo, causing oceans to absorb more solar heat and accelerate ice melt Correct answer.
  2. Increased atmospheric CO₂ accelerates plant growth, sequestering more carbon into long-term terrestrial biomass
  3. Warmer sea surface temperatures enhance mineral rock weathering, removing atmospheric CO₂ over geological timescales
  4. Increased cloud cover reflects incoming shortwave solar radiation, cooling the ground surface

Explanation

Ice-albedo feedback is positive: warming melts ice (high albedo ~0.8), exposing dark ocean water (low albedo ~0.06), which absorbs more solar radiation, triggering further thermal warming and ice loss.

Question 39Ciencias Generales

Life Cycle Assessment (LCA) studies show that Electric Vehicles (EVs) have higher manufacturing carbon emissions than internal combustion engine (ICE) vehicles. Why do EVs achieve lower overall lifecycle emissions over typical vehicle lifetimes?

  1. EVs eliminate tailpipe emissions, and operational grid charging emissions per kilometer are significantly lower than gasoline combustion Correct answer.
  2. EV batteries generate synthetic gasoline while driving down steep hills
  3. ICE vehicle engines consume zero fossil energy during urban driving
  4. EV battery manufacturing requires no raw mineral mining or refining energy

Explanation

Although lithium-ion battery manufacturing makes EV production carbon-intensive, high electric motor efficiency (~85-90% vs ICE ~20-25%) and clean grid charging enable EVs to offset their production carbon debt within 20,000–40,000 km of operation.

Question 40Ciencias Generales

In chemical absorption post-combustion Carbon Capture and Storage (CCS), which solvent class is widely used to reversibly bind flue-gas CO₂?

  1. Aqueous alkanolamines (such as monoethanolamine, MEA) Correct answer.
  2. Concentrated sulfuric acid (H₂SO₄)
  3. Liquid hydrocarbon octane (C₈H₁₈)
  4. Sodium chloride brine solution (NaCl)

Explanation

Aqueous amines like Monoethanolamine (MEA) react exothermically with CO₂ at cool temperatures (~40°C) to form carbamates; heating the solution in a stripper column (~120°C) breaks bonds, releasing pure gaseous CO₂ for sequestration.

Question 41Ciencias Generales

Which material is classified as a naturally occurring biopolymer?

  1. Cellulose Correct answer.
  2. Polyethylene terephthalate (PET)
  3. Polyvinyl chloride (PVC)
  4. Polystyrene (PS)

Explanation

Cellulose is a natural structural biopolymer synthesized by plants, composed of linear chains of \beta(1\rightarrow 4) linked D-glucose units. PET, PVC, and PS are synthetic petroleum-derived polymers.

Question 42Ciencias Generales

How do thermoplastic polymers differ from thermosetting polymers when heated?

  1. Thermoplastics melt upon heating and can be repeatedly remolded, whereas thermosets decompose without melting due to cross-linked networks Correct answer.
  2. Thermosets melt easily at room temperature, whereas thermoplastics remain permanently rigid up to 2,000 °C
  3. Thermoplastics are formed exclusively from inorganic metals, whereas thermosets consist of water crystals
  4. Thermosets can be dissolved in cold water, whereas thermoplastics react violently with air

Explanation

Thermoplastics consist of linear or branched polymer chains held by weak intermolecular forces, allowing them to melt and reform repeatedly. Thermosets contain covalent cross-links forming 3D networks that degrade irreversibly when heated.

Question 43Ciencias Generales

What is the core principle of a Circular Economy compared to a traditional Linear Economy model?

  1. Designing out waste and pollution, keeping products and materials in high-value use through repair, reuse, and recycling Correct answer.
  2. Extracting raw virgin resources, manufacturing single-use goods, and landfilling spent waste ('take-make-dispose')
  3. Maximizing municipal incineration without energy recovery
  4. Exporting all industrial electronic waste to developing countries

Explanation

A circular economy decouples economic activity from finite resource consumption by designing products for durability, reuse, remanufacturing, and closed-loop material recycling, eliminating end-of-life waste.

Question 44Ciencias Generales

Why do microplastics (< 5 mm diameter) pose a severe environmental threat in aquatic ecosystems?

  1. They are ingested by organisms, bioaccumulating up trophic food chains and adsorbing toxic hydrophobic pollutants Correct answer.
  2. They dissolve rapidly into oceanic water, raising global salinity by 15%
  3. They emit high-energy gamma radiation that sterilizes marine phytoplankton
  4. They react with sea salt to generate toxic chlorine gas clouds

Explanation

Microplastics resist degradation, persist in marine environments, and are consumed by zooplankton and fish. Their high surface area adsorbs persistent organic pollutants (POPs), biomagnifying chemical toxicity across aquatic food webs.

Question 45Ciencias Generales

What occurs during mechanical recycling of post-consumer plastic waste?

  1. Washing, shredding, melting, and extruding polymers into recycled plastic pellets without altering their chemical backbone Correct answer.
  2. Thermally breaking down polymer chains into basic crude oil monomers via high-temperature pyrolysis
  3. Incinerating plastics in open pits to generate ash fertilizer
  4. Exposing plastics to ultraviolet light to convert carbon into gaseous nitrogen

Explanation

Mechanical recycling physical reprocesses plastic waste (sorting, washing, shredding, melting, pelletizing) into new plastic items without breaking covalent polymer backbone bonds (unlike chemical recycling).

Question 46Ciencias Generales

What defines a composite material in modern engineering?

  1. A material made by combining two or more chemically distinct phases (matrix and reinforcement) to achieve superior mechanical properties Correct answer.
  2. A pure elemental metal containing a single crystal lattice structure
  3. A liquid solution formed by dissolving sugar in distilled water
  4. A biological organ composed entirely of identical single-celled bacteria

Explanation

Composites combine a binder matrix (e.g. epoxy resin) with a reinforcing phase (e.g. carbon fibers or fiberglass) to yield tailored structural properties, such as high strength-to-weight ratios.

Question 47Ciencias Generales

Polylactic acid (PLA) is a bio-based polymer synthesized from fermented plant starch. Under what conditions does industrial composting degrade PLA efficiently?

  1. High temperature (~58 °C), high humidity, and active aerobic microbial activity Correct answer.
  2. Sub-zero freezing temperatures in anaerobic dry vacuum chambers
  3. Immersion in concentrated hydrochloric acid at room temperature
  4. Exposure to intense ultraviolet radiation in outer space vacuum

Explanation

PLA requires industrial composting facility conditions: thermophilic temperatures (~55-60 °C), elevated humidity, and abundant microorganisms to hydrolyze ester bonds, breaking PLA down into water, CO₂, and biomass within months.

Question 48Ciencias Generales

Why do engineered nanomaterials (particles measuring 1 to 100 nanometers) exhibit novel physical and chemical properties compared to bulk materials of the same composition?

  1. They possess an extremely high surface-area-to-volume ratio, increasing surface atomic reactivity and quantum confinement effects Correct answer.
  2. They have zero mass and travel faster than the speed of light in a vacuum
  3. They contain no chemical bonds between constituent atoms
  4. They absorb all magnetic field lines, creating absolute room-temperature anti-gravity

Explanation

At nanoscale dimensions, a high fraction of atoms reside on the particle surface, vastly increasing chemical reactivity and catalytic activity, while quantum size confinement alters electronic, optical, and magnetic behaviors.

Question 49Ciencias Generales

Which boundary framework defines a comprehensive 'cradle-to-grave' Life Cycle Assessment (LCA) for a manufactured product?

  1. Raw material extraction → Processing → Manufacturing → Distribution → Use phase → End-of-life disposal/recycling Correct answer.
  2. Product assembly in the factory → Transportation to retail store
  3. Consumer purchase → Household storage
  4. Waste collection truck transport → Landfill capping

Explanation

A full cradle-to-grave LCA evaluates environmental impacts across the complete lifecycle: raw resource extraction, refining, production, transport, operational use phase, and final recycling or waste disposal.

Question 50Ciencias Generales

Why is the recycling of electronic waste (e-waste) critical for green technology supply chains?

  1. It recovers critical raw materials (e.g., lithium, cobalt, rare earth elements) whose primary mining causes severe environmental degradation and supply risks Correct answer.
  2. E-waste naturally generates pure gold crystals when left in municipal landfills
  3. Recycling e-waste consumes zero energy compared to leaving electronics in household drawers
  4. Electronic components degrade into organic compost within 24 hours of disposal

Explanation

Electronics contain scarce critical raw materials (lithium, cobalt, neodymium, indium). Recycling e-waste conserves natural ore deposits, reduces toxic heavy metal leaching (lead, mercury), and secures sustainable material loops.