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ILTS Science: Chemistry (240) study materials
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ILTS Science: Chemistry (240) practice questions

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Question 1Foundations of Scientific Inquiry and the Nature of Science

A student claims that a hypothesis becomes a scientific theory once it has been tested many times. Which statement best corrects this misconception about the nature of science?

  1. A theory and a hypothesis are interchangeable terms that differ only in the length of the written statement.
  2. A theory is an untested guess, and a hypothesis is the explanation that has survived repeated testing.
  3. A theory becomes a scientific law once enough experiments are performed, replacing the hypothesis entirely.
  4. A theory is a broad, well-supported explanation of many observations, whereas a hypothesis is a specific, testable prediction. Correct answer.

Explanation

In science, a theory is a comprehensive explanatory framework supported by extensive evidence and multiple lines of investigation, not a stepping stone that a single hypothesis graduates into. A hypothesis is a narrow, testable prediction or provisional explanation. Laws and theories serve different functions, and evidence accumulation does not convert one into the other.

Question 2Foundations of Scientific Inquiry and the Nature of Science

A researcher designs an experiment to test whether a new fertilizer increases tomato yield. Which procedure best ensures the results can be attributed to the fertilizer rather than to other variables?

  1. Give all plants the fertilizer and record the yield at the end of the season.
  2. Assign identical plants randomly to fertilized and unfertilized groups and control light, water, and soil. Correct answer.
  3. Use plants of different species so that the results apply to a wider range of crops.
  4. Measure the yield only on the plants that appear healthiest during the growing season.

Explanation

A controlled experiment holds all variables constant except the independent variable, and random assignment distributes uncontrolled variation across groups. Comparing fertilized and unfertilized groups of identical plants isolates the fertilizer's effect. Without a control group or with confounded variables, the cause of any yield difference cannot be identified.

Question 3Foundations of Scientific Inquiry and the Nature of Science

Which statement accurately describes the role of peer review in the scientific process?

  1. It replaces the need for replication because reviewers independently repeat the experiments.
  2. It is a formality performed by the journal's editors without evaluating scientific content.
  3. It evaluates the study's methods and reasoning before publication, though errors can still be found later. Correct answer.
  4. It guarantees that a published study's conclusions are correct and will never be revised.

Explanation

Peer review is a quality-control step in which independent experts assess the design, evidence, and reasoning of a manuscript before publication. It improves but does not guarantee correctness, and published findings may later be revised or retracted. Replication by other scientists remains a separate and essential check.

Question 4Foundations of Scientific Inquiry and the Nature of Science

A student records the volume of a liquid as 24.6 mL using a graduated cylinder marked in 1 mL increments. Which statement about this measurement is most accurate?

  1. The measurement is exact because the student read the meniscus carefully.
  2. The measurement should be reported as 25 mL because the cylinder is marked in 1 mL increments.
  3. The measurement has an uncertainty of zero because the cylinder is a precise instrument.
  4. The measurement has three significant figures, with the final digit estimated. Correct answer.

Explanation

When reading an analog scale, the last recorded digit is an estimate between the smallest markings, so 24.6 mL contains three significant figures. All measurements carry uncertainty, and reporting to the estimated digit preserves the instrument's precision. Rounding to 25 mL would discard meaningful information about the reading.

Question 5Foundations of Scientific Inquiry and the Nature of Science

In a controlled experiment, which variable is deliberately changed by the investigator to observe its effect?

  1. The independent variable Correct answer.
  2. The confounding variable
  3. The control variable
  4. The dependent variable

Explanation

The independent variable is the factor the investigator manipulates, and the dependent variable is the response measured. Control variables are held constant to prevent confounding. Confounding variables are unintended factors that can distort the relationship being studied.

Question 6Foundations of Scientific Inquiry and the Nature of Science

A scientific model of a chemical process is useful primarily because it does which of the following?

  1. Reproduces every detail of the real system with complete accuracy.
  2. Simplifies and represents key features of a system to explain observations and make predictions. Correct answer.
  3. Replaces the need for experimental evidence once it is constructed.
  4. Provides a permanent explanation that is never modified by new data.

Explanation

Models are deliberate simplifications that highlight the features relevant to a question, allowing scientists to explain observations and generate testable predictions. Because they are simplifications, models are revised when new evidence appears. They supplement rather than replace empirical investigation.

Question 7Foundations of Scientific Inquiry and the Nature of Science

Which practice most directly reflects the ethical obligation of scientists to report findings honestly?

  1. Publishing only the trials that produced statistically significant results.
  2. Adjusting data points that appear inconsistent with the hypothesis.
  3. Describing the methods and limitations of a study accurately, including unexpected results. Correct answer.
  4. Listing collaborators as authors without their knowledge to acknowledge their help.

Explanation

Scientific integrity requires transparent reporting of methods, limitations, and all relevant results, including those that do not support the hypothesis. Selectively reporting only favorable outcomes or altering data misrepresents the evidence. Authorship must also be based on consent and genuine contribution.

Question 8Foundations of Scientific Inquiry and the Nature of Science

A student measures the density of an unknown metal three times and obtains 7.82, 7.85, and 7.83 g/cm3, while the accepted value is 8.96 g/cm3. How should these results be described?

  1. Neither accurate nor precise
  2. Both accurate and precise
  3. Precise but not accurate Correct answer.
  4. Accurate but not precise

Explanation

Precision refers to how closely repeated measurements agree with one another, and these three values are tightly clustered, so they are precise. Accuracy refers to closeness to the accepted value, and all three differ from 8.96 g/cm3 by more than 1 g/cm3, so they are not accurate. A systematic error, such as a miscalibrated instrument, often produces this pattern.

Question 9Foundations of Scientific Inquiry and the Nature of Science

A graph plots reaction rate on the y-axis against substrate concentration on the x-axis, and the curve rises steeply then levels off at high substrate concentration. Which conclusion is best supported by this pattern?

  1. The rate becomes independent of substrate concentration at high concentration, suggesting enzyme saturation. Correct answer.
  2. The reaction rate decreases as substrate concentration increases.
  3. Substrate concentration has no effect on reaction rate at any concentration.
  4. The reaction rate increases without limit as substrate concentration increases.

Explanation

The plateau indicates that the rate stops increasing once the enzyme's active sites are saturated, so additional substrate no longer raises the rate. This saturation behavior is characteristic of enzyme-catalyzed reactions and supports a maximum rate. The initial steep rise shows that substrate concentration does affect the rate at lower concentrations.

Question 10Foundations of Scientific Inquiry and the Nature of Science

A scientist proposes that a new drug lowers blood pressure by inhibiting a specific enzyme. Which observation would provide the strongest support for this proposed mechanism?

  1. The drug is chemically similar to another drug known to lower blood pressure.
  2. The drug lowers blood pressure in some patients but not in others.
  3. Blood pressure falls with increasing drug dose, and enzyme activity measured in blood decreases in parallel. Correct answer.
  4. Patients taking the drug report feeling better than patients taking a placebo.

Explanation

A dose-response relationship combined with a corresponding change in the proposed target provides direct mechanistic evidence linking the drug to enzyme inhibition and the physiological effect. This supports the causal pathway rather than merely correlating the drug with an outcome. Subjective reports or structural similarity alone are weaker evidence.

Question 11Foundations of Scientific Inquiry and the Nature of Science

A student wants to determine how temperature affects the solubility of a solid in water. Which set of conditions should be varied and which held constant?

  1. Vary the water temperature and hold the amount of water, solute type, and stirring constant. Correct answer.
  2. Vary the water temperature and the amount of water simultaneously to save time.
  3. Vary the solute type and hold the temperature constant.
  4. Vary the amount of solute and hold the water temperature constant.

Explanation

To isolate the effect of temperature, only temperature should be changed while other factors that influence solubility, such as solvent amount, solute identity, and stirring, are held constant. Changing two variables at once confounds the results. The question asks specifically about temperature, so solute amount and type must remain fixed.

Question 12Foundations of Scientific Inquiry and the Nature of Science

A claim states that a chemical is safe because no study has shown it to be harmful. Which principle of scientific reasoning does this claim violate?

  1. The principle that all hypotheses must be falsifiable
  2. The principle that correlation implies causation
  3. The principle that absence of evidence is not evidence of absence Correct answer.
  4. The principle that measurements must be precise

Explanation

Lacking evidence of harm does not establish that something is safe; it may reflect that adequate studies have not been done. This is the classic distinction between absence of evidence and evidence of absence. Sound reasoning requires positive evidence, not merely the absence of contrary findings.

Question 13Foundations of Scientific Inquiry and the Nature of Science

Which statement best explains why scientific knowledge is described as tentative?

  1. Scientific knowledge is tentative only until it is published in a textbook.
  2. Scientific conclusions are based on the opinions of influential researchers.
  3. Scientific laws are eventually proven and then never change.
  4. Scientific explanations can be revised when new evidence or better methods become available. Correct answer.

Explanation

Tentativeness reflects the self-correcting nature of science: conclusions are always open to revision in light of new evidence, improved instruments, or better models. This does not mean scientific knowledge is unreliable, only that it is provisional and evidence-dependent. Publication or textbook inclusion does not make a claim permanent.

Question 14Foundations of Scientific Inquiry and the Nature of Science

A researcher reports a result with a p-value of 0.03. Which interpretation is most appropriate?

  1. The result has a 97% probability of being replicated in a future study.
  2. Assuming the null hypothesis is true, there is a 3% probability of obtaining a result at least as extreme as observed. Correct answer.
  3. The effect size is large enough to be practically important.
  4. There is a 3% probability that the null hypothesis is true.

Explanation

A p-value is the probability of observing data at least as extreme as the obtained result, calculated under the assumption that the null hypothesis is true. It is not the probability that the null hypothesis is true, nor a direct measure of replication probability or practical importance. Those interpretations require additional information such as effect size and study design.

Question 15Foundations of Scientific Inquiry and the Nature of Science

A student uses a balance that reads 0.00 g when empty but consistently reads 0.50 g too high for every sample. This instrument error primarily affects which aspect of the measurements?

  1. Neither accuracy nor precision, because the error is constant
  2. Random error, because the shift varies unpredictably
  3. Accuracy, because all readings are shifted by a constant amount Correct answer.
  4. Precision, because repeated readings will vary widely

Explanation

A constant offset is a systematic error that shifts every measurement in the same direction, reducing accuracy while leaving precision largely unaffected. Repeated readings would still cluster tightly, but around the wrong value. Calibration would correct this systematic bias.

Question 16Foundations of Scientific Inquiry and the Nature of Science

Which feature of a scientific investigation most directly strengthens the external validity of its conclusions?

  1. Increasing the number of significant figures reported for each measurement
  2. Reporting only results that agree with the original hypothesis
  3. Conducting all trials in a single laboratory by one researcher
  4. Using a large sample drawn to represent the population to which the results will be generalized Correct answer.

Explanation

External validity concerns how well findings generalize beyond the study sample, and a representative sample supports that generalization. Larger samples also improve precision, but representativeness is the key issue for generalizability. Reporting conventions and single-site execution do not address generalization.

Question 17Foundations of Scientific Inquiry and the Nature of Science

A student calculates a result of 0.004560 kg from measured values. How many significant figures does this value have?

  1. Seven
  2. Four Correct answer.
  3. Three
  4. Six

Explanation

Leading zeros are not significant, so 0.004560 begins with the digits 4, 5, 6, and the trailing zero after the 6 is significant because it follows a decimal point. That gives four significant figures. The leading zeros merely locate the decimal point.

Question 18Foundations of Scientific Inquiry and the Nature of Science

A scientist repeats an experiment and obtains results that contradict an earlier published finding. What is the most appropriate scientific response?

  1. Ignore the discrepancy to avoid challenging established researchers.
  2. Publish the new results only after modifying them to match the earlier finding.
  3. Investigate differences in methods and conditions, then report the discrepancy with supporting evidence. Correct answer.
  4. Assume the new results are wrong because the earlier study was published.

Explanation

Contradictory results are handled by examining methodological differences and reporting the evidence transparently so the community can evaluate it. Discrepancies often reveal hidden variables or limits on earlier conclusions. Modifying data or ignoring contradictions violates scientific integrity.

Question 19Foundations of Scientific Inquiry and the Nature of Science

A class investigates whether light intensity affects the rate of photosynthesis in aquatic plants. Which dependent variable and measurement method are most appropriate?

  1. Water temperature, measured with a thermometer throughout the trial
  2. Number of oxygen bubbles produced per minute at each light intensity Correct answer.
  3. Plant species, chosen to represent common aquarium plants
  4. Light intensity, measured with a light meter at each distance

Explanation

The dependent variable is the response to the manipulated factor, so the rate of photosynthesis must be measured. Counting oxygen bubbles per minute provides a quantifiable proxy for photosynthetic rate. Light intensity is the independent variable, and temperature and species are controlled variables.

Question 20Foundations of Scientific Inquiry and the Nature of Science

A student claims that because two variables are strongly correlated across a data set, one must cause the other. Which additional consideration is most important before accepting a causal claim?

  1. Whether the data were graphed with a line of best fit
  2. Whether a plausible mechanism exists and confounding variables have been ruled out Correct answer.
  3. Whether the correlation coefficient was calculated with a spreadsheet
  4. Whether the sample size was reported to three significant figures

Explanation

Correlation alone cannot establish causation because a third variable may drive both, or the relationship may be coincidental. A credible causal claim requires ruling out confounders and ideally identifying a mechanism supported by controlled evidence. Computational or formatting details do not strengthen causal inference.

Question 21Foundations of Scientific Inquiry and the Nature of Science

In a double-blind clinical trial, neither participants nor the researchers assessing outcomes know who receives the treatment. What is the primary purpose of this design?

  1. To reduce bias from participant expectations and from researchers' scoring of outcomes Correct answer.
  2. To guarantee that the treatment is effective in the general population
  3. To increase the sample size without additional cost
  4. To eliminate the need for a control group

Explanation

Blinding prevents expectancy effects and conscious or unconscious bias in how outcomes are assessed, which protects the validity of the comparison. Double blinding does not increase sample size or guarantee effectiveness. A control group is still essential to the design.

Question 22Foundations of Scientific Inquiry and the Nature of Science

A researcher reports a mean of 50 with a 95% confidence interval of 46 to 54. A second study reports a mean of 50 with a 95% confidence interval of 49 to 51. Which conclusion is best supported?

  1. Both studies estimated the same population mean with equal precision.
  2. The first study's wider interval proves its result is incorrect.
  3. The confidence intervals indicate that the two studies measured different populations.
  4. The second study's estimate is more precise, though both are centered on the same value. Correct answer.

Explanation

A narrower confidence interval indicates a more precise estimate, often due to a larger sample or less variability, while the point estimate remains the same. A wider interval does not mean the result is wrong; it reflects greater uncertainty. Both intervals overlap around 50, so they are consistent with the same population mean.

Question 23Foundations of Scientific Inquiry and the Nature of Science

A model predicts that a reaction will produce a specific product, but experimental analysis reveals an unexpected side product. Which response best reflects how scientific models function?

  1. Report the prediction as confirmed because the model was based on accepted theory.
  2. Discard the model entirely, since any failed prediction invalidates all of its useful features.
  3. Use the discrepancy to refine the model by identifying overlooked variables or competing pathways. Correct answer.
  4. Adjust the experimental data so that the predicted product appears to be the only one formed.

Explanation

Models are judged by their explanatory and predictive usefulness, and discrepancies often reveal missing factors such as competing reaction pathways. Refining the model in light of evidence is a normal part of scientific progress. Discarding all value or altering data misrepresents how models and evidence interact.

Question 24Foundations of Scientific Inquiry and the Nature of Science

A study finds that students who eat breakfast score higher on a chemistry exam than students who skip breakfast. Which factor most threatens the internal validity of a causal conclusion that breakfast improves exam scores?

  1. The exam included both multiple-choice and free-response items.
  2. The study reported scores as percentages rather than raw points.
  3. Students who eat breakfast may differ systematically in study habits, sleep, or socioeconomic status. Correct answer.
  4. The exam was administered in the morning.

Explanation

Internal validity requires ruling out alternative explanations for the observed difference. If breakfast eaters differ systematically in study habits, sleep, or resources, those factors could drive the score difference rather than breakfast itself. This is confounding by self-selection, since students were not randomly assigned.

Question 25Chemistry Content: Matter, Atomic Structure, and Periodicity

A neutral atom of an element has 16 protons and 18 neutrons. What is the mass number of this atom?

  1. 2
  2. 34 Correct answer.
  3. 18
  4. 16

Explanation

The mass number is the sum of protons and neutrons in the nucleus, so 16 + 18 = 34. The number of protons alone identifies the element (atomic number 16, sulfur), not the mass number.

Question 26Chemistry Content: Matter, Atomic Structure, and Periodicity

Which subatomic particle determines the identity of an element?

  1. The proton Correct answer.
  2. The positron
  3. The neutron
  4. The electron

Explanation

The atomic number equals the number of protons, and this value uniquely identifies each element on the periodic table. Changing the proton count converts the atom into a different element.

Question 27Chemistry Content: Matter, Atomic Structure, and Periodicity

An atom of an element has the electron configuration 1s² 2s² 2p⁶ 3s¹. In which period and group does this element appear?

  1. Period 3, Group 1 Correct answer.
  2. Period 2, Group 1
  3. Period 3, Group 3
  4. Period 1, Group 3

Explanation

The highest occupied principal level is n = 3, so the element is in period 3. The single valence electron in the 3s orbital places it in Group 1, which is sodium.

Question 28Chemistry Content: Matter, Atomic Structure, and Periodicity

Which statement correctly describes the trend in atomic radius across a period from left to right?

  1. Radius increases because more electrons are added to the atom.
  2. Radius stays constant because the number of shells does not change.
  3. Radius decreases because the number of neutrons increases.
  4. Radius decreases because effective nuclear charge increases while electrons enter the same shell. Correct answer.

Explanation

Across a period, protons are added to the nucleus while electrons enter the same principal shell, so effective nuclear charge rises and pulls the electron cloud inward. The result is a smaller atomic radius from left to right.

Question 29Chemistry Content: Matter, Atomic Structure, and Periodicity

Which of the following is classified as a homogeneous mixture?

  1. A suspension of sand in water
  2. A granite rock
  3. A mixture of oil and water
  4. Salt water Correct answer.

Explanation

A homogeneous mixture has a uniform composition throughout, and dissolved salt in water forms a single phase. The other examples contain visibly distinct phases or settle over time.

Question 30Chemistry Content: Matter, Atomic Structure, and Periodicity

Which group of the periodic table contains the halogens?

  1. Group 1
  2. Group 2
  3. Group 17 Correct answer.
  4. Group 18

Explanation

The halogens occupy Group 17 and have seven valence electrons, making them highly reactive nonmetals. Group 18 elements are the noble gases, and Groups 1 and 2 are the alkali and alkaline earth metals.

Question 31Chemistry Content: Matter, Atomic Structure, and Periodicity

A sample of a pure element conducts electricity, is malleable, and has a high melting point. Which type of bonding best explains these properties?

  1. Metallic bonding Correct answer.
  2. Ionic bonding
  3. Covalent network bonding
  4. Intermolecular hydrogen bonding

Explanation

Metallic bonding involves delocalized valence electrons shared among a lattice of cations, which accounts for electrical conductivity, malleability, and high melting points. Covalent networks are hard but brittle and usually nonconducting.

Question 32Chemistry Content: Matter, Atomic Structure, and Periodicity

Which quantity is conserved in a balanced chemical equation?

  1. The total volume of reactants and products
  2. The number of atoms of each element Correct answer.
  3. The number of moles of gaseous species
  4. The number of molecules on each side

Explanation

Balancing a chemical equation enforces the law of conservation of mass, which requires equal numbers of atoms of each element on both sides. Molecular counts, volumes, and gas mole totals are not generally conserved.

Question 33Chemistry Content: Matter, Atomic Structure, and Periodicity

How many significant figures are present in the measured value 0.004250 g?

  1. Five
  2. Two
  3. Four Correct answer.
  4. Three

Explanation

Leading zeros are placeholders and are not significant, so the count begins at the 4. The digits 4, 2, 5, and the trailing zero after the decimal are all significant, giving four.

Question 34Chemistry Content: Matter, Atomic Structure, and Periodicity

A neutral atom has 24 protons and 28 neutrons. How many electrons occupy its 3d subshell?

  1. 6
  2. 2
  3. 5 Correct answer.
  4. 4

Explanation

With 24 electrons, the configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d⁵ by the aufbau order, so the 3d subshell holds five electrons. Chromium's half-filled d subshell is a well-known exception to the simple filling pattern.

Question 35Chemistry Content: Matter, Atomic Structure, and Periodicity

Which element has the largest first ionization energy?

  1. Neon Correct answer.
  2. Argon
  3. Magnesium
  4. Sodium

Explanation

First ionization energy generally increases across a period and peaks at the noble gases, but neon's small size and tightly held 2p electrons give it a higher value than argon. Sodium and magnesium lose electrons far more readily than the noble gases.

Question 36Chemistry Content: Matter, Atomic Structure, and Periodicity

Which species has the same electron configuration as the argon atom?

  1. Cl
  2. S²⁻ Correct answer.
  3. Na⁺
  4. Mg

Explanation

The sulfide ion has gained two electrons, giving it 18 electrons, which matches argon's configuration. A neutral chlorine atom has 17 electrons, and the magnesium atom has 12.

Question 37Chemistry Content: Matter, Atomic Structure, and Periodicity

Which property increases from left to right across a period of the periodic table?

  1. Atomic radius
  2. Metallic character
  3. Electronegativity Correct answer.
  4. Number of occupied principal shells

Explanation

Electronegativity rises across a period as effective nuclear charge increases and atoms attract bonding electrons more strongly. Atomic radius, metallic character, and shell count do not increase in this direction.

Question 38Chemistry Content: Matter, Atomic Structure, and Periodicity

Which pair of elements would be expected to form an ionic compound with the formula XY₂, where X is a Group 2 metal and Y is a Group 17 nonmetal?

  1. Calcium and oxygen
  2. Potassium and chlorine
  3. Calcium and chlorine Correct answer.
  4. Sulfur and chlorine

Explanation

Calcium forms a 2+ ion and chlorine forms a 1− ion, so charge balance requires two chloride ions per calcium ion, giving CaCl₂. Potassium chloride forms a 1:1 ratio, and calcium oxide forms a 1:1 ratio.

Question 39Chemistry Content: Matter, Atomic Structure, and Periodicity

A sample of a compound contains 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. What is its empirical formula?

  1. C₂H₄O
  2. CH₂O Correct answer.
  3. CH₄O
  4. CHO

Explanation

Dividing each percentage by the atomic mass gives 3.33 mol C, 6.7 mol H, and 3.33 mol O. Dividing by the smallest value yields a 1:2:1 ratio, so the empirical formula is CH₂O.

Question 40Chemistry Content: Matter, Atomic Structure, and Periodicity

Which observation provides the strongest evidence that a new substance has formed rather than a physical change occurring?

  1. A gas is produced that has a different odor from the original reactants. Correct answer.
  2. A colored solution is diluted with water.
  3. A solid is ground into a finer powder.
  4. A liquid is heated until it boils.

Explanation

Production of a new gas with different properties indicates a chemical reaction in which new substances form. Grinding, boiling, and dilution alter only physical state or concentration without changing chemical identity.

Question 41Chemistry Content: Matter, Atomic Structure, and Periodicity

Which set of quantum numbers is permissible for an electron in an atom?

  1. n = 3, l = 3, mₗ = 0, mₛ = +½
  2. n = 4, l = 2, mₗ = −3, mₛ = +½
  3. n = 2, l = 0, mₗ = 1, mₛ = −½
  4. n = 3, l = 2, mₗ = −1, mₛ = +½ Correct answer.

Explanation

The rules require l < n and −l ≤ mₗ ≤ +l, and the first set satisfies both with l = 2 and mₗ = −1. The other sets violate the l or mₗ limits.

Question 42Chemistry Content: Matter, Atomic Structure, and Periodicity

Which statement best explains why the second ionization energy of magnesium is much higher than its first?

  1. The second electron is removed from a cation, so it experiences a stronger net attraction to the nucleus. Correct answer.
  2. The second electron is removed from a higher principal shell than the first.
  3. Ionization energy decreases as successive electrons are removed.
  4. The first electron removed is a core electron rather than a valence electron.

Explanation

After one electron is lost, the remaining electrons are held more tightly by the same nuclear charge, so removing the next electron requires much more energy. Successive ionization energies therefore increase rather than decrease.

Question 43Chemistry Content: Matter, Atomic Structure, and Periodicity

A 2.50 g sample of a metal is heated and placed in a calorimeter, and 1.20 kJ of heat is released. What is the specific heat of the metal if its temperature rises by 40.0 °C?

  1. 48.0 J/(g·°C)
  2. 8.0 J/(g·°C)
  3. 12.0 J/(g·°C) Correct answer.
  4. 0.083 J/(g·°C)

Explanation

Using q = mcΔT, solve for c = q/(mΔT) = 1200 J / (2.50 g × 40.0 °C) = 12.0 J/(g·°C). The heat must be converted to joules before dividing.

Question 44Chemistry Content: Matter, Atomic Structure, and Periodicity

Which explanation correctly accounts for the decrease in first ionization energy from beryllium to boron?

  1. Boron's valence electron is in the 3s orbital, farther from the nucleus.
  2. Boron's outermost electron occupies a 2p orbital, which is higher in energy and better shielded than the 2s orbital. Correct answer.
  3. Boron has a larger nuclear charge, which weakens its hold on electrons.
  4. Beryllium has one more electron shell than boron.

Explanation

Beryllium's valence electrons occupy the filled 2s subshell, while boron's fifth electron enters a 2p orbital that lies higher in energy and is shielded by the 2s electrons. This makes boron's electron easier to remove despite its larger nuclear charge.

Question 45Chemistry Content: Matter, Atomic Structure, and Periodicity

Which pair of elements shows the most pronounced diagonal relationship in periodic properties?

  1. Fluorine and neon
  2. Beryllium and boron
  3. Sodium and magnesium
  4. Lithium and magnesium Correct answer.

Explanation

Lithium and magnesium exhibit a classic diagonal relationship, sharing similarities such as carbonate decomposition behavior and nitride formation. Diagonal relationships arise from comparable charge-to-size ratios across adjacent groups and periods.

Question 46Chemistry Content: Matter, Atomic Structure, and Periodicity

An element has a first ionization energy of 738 kJ/mol, a second of 1451 kJ/mol, and a third of 7733 kJ/mol. To which group does this element most likely belong?

  1. Group 13
  2. Group 17
  3. Group 1
  4. Group 2 Correct answer.

Explanation

The large jump between the second and third ionization energies indicates that the third electron is removed from a stable noble-gas core. Two relatively low ionization energies point to two valence electrons, consistent with Group 2.

Question 47Chemistry Content: Matter, Atomic Structure, and Periodicity

Which comparison of the ionic radii of Na⁺, Mg²⁺, and F⁻ is correct?

  1. Na⁺ < Mg²⁺ < F⁻
  2. Mg²⁺ < Na⁺ < F⁻ Correct answer.
  3. F⁻ < Na⁺ < Mg²⁺
  4. Mg²⁺ < F⁻ < Na⁺

Explanation

All three ions are isoelectronic with neon, so radius depends on nuclear charge: more protons pull the electrons in more tightly. Mg²⁺ has 12 protons and is smallest, Na⁺ has 11, and F⁻ has only 9 and is largest.

Question 48Chemistry Content: Matter, Atomic Structure, and Periodicity

A certain element's highest-energy electron has quantum numbers n = 4, l = 0. Which conclusion about the element is most defensible?

  1. It is a noble gas with a filled 4p subshell.
  2. It is a halogen located in Group 17.
  3. It is a period 4 element with its outer electron in an s orbital, likely a Group 1 or 2 metal. Correct answer.
  4. It is a transition metal with a partially filled 3d subshell.

Explanation

The value l = 0 identifies an s orbital, and n = 4 places the valence electron in the fourth period. Elements whose last electron enters the 4s orbital are the period 4 s-block metals in Groups 1 and 2.

Question 49Chemistry Content: Matter, Atomic Structure, and Periodicity

Which statement correctly distinguishes isotopes of the same element?

  1. They have identical electron configurations in all ionization states.
  2. They have identical mass numbers but different proton counts.
  3. They have identical proton counts but different neutron counts, giving different mass numbers. Correct answer.
  4. They have identical neutron counts but different proton counts.

Explanation

Isotopes are atoms of the same element, so they share the same number of protons while differing in neutrons and therefore mass number. Their chemical behavior is nearly identical, but their nuclear masses differ.

Question 50Chemistry Content: Matter, Atomic Structure, and Periodicity

A neutral atom of an element in its ground state has the electron configuration 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁴. In which block and group of the periodic table is this element located?

  1. d block, Group 10
  2. s block, Group 2
  3. p block, Group 14
  4. p block, Group 16 Correct answer.

Explanation

The highest-energy electrons are in the 4p subshell, so the element is in the p block. The valence configuration is 4s² 4p⁴, giving six valence electrons and placing the element in Group 16 (the chalcogens).