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MTTC Chemistry (018) study materials
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MTTC Chemistry (018) practice questions

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Question 1Scientific Inquiry and the Processes of Chemistry

In chemistry, which statement best describes a hypothesis?

  1. A broad explanation supported by a large body of evidence.
  2. A statement that has been proven true beyond any doubt.
  3. A testable prediction that can be supported or refuted by experiment. Correct answer.
  4. A personal belief that cannot be tested.

Explanation

A hypothesis is a tentative, testable explanation or prediction that guides an experiment. It is not a proven fact, a broad theory, or an untestable opinion. Experimental results can support or refute it.

Question 2Scientific Inquiry and the Processes of Chemistry

A student investigates how temperature affects the rate of a chemical reaction. Which variable is the independent variable in this experiment?

  1. The time required for the reaction to finish.
  2. The amount of reactant used.
  3. The temperature of the reaction mixture. Correct answer.
  4. The rate of the reaction.

Explanation

The independent variable is the factor that the experimenter deliberately changes. In this design, temperature is manipulated while the reaction rate is measured as the dependent variable. Reactant amount and time are held constant or measured.

Question 3Scientific Inquiry and the Processes of Chemistry

Which laboratory practice is appropriate when heating a liquid in a test tube?

  1. Fill the test tube to the top before heating.
  2. Point the test tube mouth away from people. Correct answer.
  3. Hold the test tube with your bare hand while heating.
  4. Stopper the test tube tightly before heating.

Explanation

Heating a test tube can cause bumping or ejection of hot liquid, so the open mouth should be directed away from people. Test tubes should never be filled completely or tightly stoppered when heated. A test-tube holder protects the hand.

Question 4Scientific Inquiry and the Processes of Chemistry

Perform the calculation and report the answer with the correct number of significant figures: (2.34 × 1.2) + 0.003.

  1. 2.808
  2. 2.8 Correct answer.
  3. 2.81
  4. 2.803

Explanation

The multiplication 2.34 × 1.2 gives 2.808, which is limited to two significant figures by 1.2, so it becomes 2.8. Adding 0.003 is limited to the tenths place, so the final answer remains 2.8.

Question 5Scientific Inquiry and the Processes of Chemistry

A student weighs a sample three times and obtains 5.01 g, 5.02 g, and 5.01 g. The accepted value is 5.50 g. Which statement best describes the measurements?

  1. The measurements are neither precise nor accurate.
  2. The measurements are both precise and accurate.
  3. The measurements are accurate but not precise.
  4. The measurements are precise but not accurate. Correct answer.

Explanation

Precision refers to how close repeated measurements are to one another, while accuracy refers to closeness to the accepted value. The three values cluster tightly together but are about 0.49 g below the accepted value. Therefore they are precise but not accurate.

Question 6Scientific Inquiry and the Processes of Chemistry

A student measures the mass of a product as 9.8 g, but the accepted value is 10.0 g. What is the percent error of the student's measurement?

  1. 20%
  2. 0.02%
  3. 0.2%
  4. 2% Correct answer.

Explanation

Percent error is calculated as |measured - accepted| / accepted × 100%. Substituting gives |9.8 - 10.0| / 10.0 × 100% = 0.2 / 10.0 × 100% = 2%. The sign is removed by the absolute value.

Question 7Scientific Inquiry and the Processes of Chemistry

A student measures 25.0 mL of solution. What is this volume expressed in liters?

  1. 25,000 L
  2. 0.250 L
  3. 2.50 L
  4. 0.0250 L Correct answer.

Explanation

One liter equals 1000 milliliters, so the volume in liters is 25.0 divided by 1000. Moving the decimal point three places to the left gives 0.0250 L. The significant figures are preserved in the conversion.

Question 8Scientific Inquiry and the Processes of Chemistry

In an experiment testing a new fertilizer, one group of plants receives the fertilizer and another group receives only water. What is the main purpose of the water-only group?

  1. It serves as a control for the fertilized group. Correct answer.
  2. It directly measures the dependent variable for the fertilized group.
  3. It increases the sample size to improve precision.
  4. It provides an additional level of the fertilizer treatment.

Explanation

The water-only group is a control that isolates the effect of the fertilizer by keeping other factors constant. Comparing the fertilized group with this control shows whether the fertilizer caused any observed change. The control is not an extra fertilizer level or a precision boost.

Question 9Scientific Inquiry and the Processes of Chemistry

A student plots ln(k) versus 1/T for a reaction and obtains a straight line with slope -5000 K. Using the Arrhenius relationship slope = -Ea/R and R = 8.314 J/(mol·K), what is the activation energy Ea?

  1. 4.16 kJ/mol
  2. 60.1 kJ/mol
  3. 41.6 kJ/mol Correct answer.
  4. 0.60 kJ/mol

Explanation

Rearranging the Arrhenius slope relationship gives Ea = -slope × R. Substituting -(-5000 K) × 8.314 J/(mol·K) yields about 41,570 J/mol, which is 41.6 kJ/mol. The units of K in the slope cancel with the gas constant to leave J/mol.

Question 10Scientific Inquiry and the Processes of Chemistry

A pH meter that is not calibrated consistently reads 0.3 pH units too high for every sample tested. This type of measurement problem is best classified as which of the following?

  1. Sampling error
  2. Human blunder
  3. Random error
  4. Systematic error Correct answer.

Explanation

Systematic error produces a consistent bias in one direction, such as always reading 0.3 pH units too high because of improper calibration. Random error would scatter readings unpredictably around the true value. A blunder is a one-time mistake, and sampling error concerns which samples were selected.

Question 11Scientific Inquiry and the Processes of Chemistry

In a controlled chemistry experiment, why are variables other than the independent variable held constant?

  1. To reduce the total time needed to complete all planned trials
  2. To attribute observed effects to the independent variable Correct answer.
  3. To remove the need for a stated hypothesis
  4. To guarantee statistically significant results

Explanation

Holding other variables constant prevents them from changing the outcome and creating alternative explanations. This control lets the experimenter connect changes in the dependent variable to the independent variable rather than to a confounding factor.

Question 12Scientific Inquiry and the Processes of Chemistry

Before a student uses an unfamiliar chemical in the laboratory, which action is most appropriate?

  1. Smell the chemical directly to identify it
  2. Store it in an unmarked food container to prevent breakage
  3. Dilute it with water before checking its label
  4. Review the safety data sheet for hazards and handling Correct answer.

Explanation

A safety data sheet provides information on hazards, handling, storage, and emergency measures for a chemical. Reviewing it before use is a standard laboratory safety practice that helps prevent exposure and accidents.

Question 13Scientific Inquiry and the Processes of Chemistry

When reading the volume of a clear liquid in a burette, where should the observer's eye be placed?

  1. Level with the meniscus Correct answer.
  2. Below the meniscus, looking upward
  3. Above the meniscus, looking downward
  4. At the stopcock, looking along the burette

Explanation

The eye should be level with the meniscus to avoid parallax error, which occurs when the scale and liquid surface are viewed from an angle. Viewing at eye level gives the most accurate volume reading.

Question 14Scientific Inquiry and the Processes of Chemistry

A calibration plot of absorbance versus concentration is described by y = 0.025x + 0.010, where x is concentration in mg/L and y is absorbance. What concentration corresponds to an absorbance of 0.310?

  1. 12.0 mg/L Correct answer.
  2. 10.0 mg/L
  3. 12.5 mg/L
  4. 8.0 mg/L

Explanation

Substitute y = 0.310 into the calibration equation and solve for x: 0.310 = 0.025x + 0.010, so 0.300 = 0.025x and x = 12.0 mg/L. The intercept must be subtracted before dividing by the slope.

Question 15Scientific Inquiry and the Processes of Chemistry

For a fixed amount of ideal gas at constant temperature, a graph of pressure P versus 1/V is linear. What does the slope of this graph represent?

  1. RT/n
  2. nR/T
  3. nRT Correct answer.
  4. 1/nRT

Explanation

The ideal gas law gives P = nRT(1/V) when temperature and amount are constant. Therefore a plot of P versus 1/V has slope nRT.

Question 16Scientific Inquiry and the Processes of Chemistry

A student tests how catalyst concentration affects reaction rate by running all low-concentration trials first and all high-concentration trials last. Room temperature rises during the session. What is the main problem with this design?

  1. The student has not included enough different concentrations
  2. The catalyst concentration is not measured precisely enough in each trial
  3. The order of trials confounds concentration with temperature Correct answer.
  4. The reaction rate is not a dependent variable

Explanation

Because temperature changes over time, running all low-concentration trials first and high-concentration trials last ties catalyst concentration to the temperature drift. Any rate difference could then be due to temperature rather than catalyst concentration.

Question 17Scientific Inquiry and the Processes of Chemistry

In a formal laboratory report for a chemistry experiment, which section is the most appropriate place to analyze the effect of random measurement error on the results?

  1. Title
  2. Discussion Correct answer.
  3. Procedure
  4. Reference list

Explanation

The discussion section interprets results, evaluates sources of error, and explains how uncertainty affects the conclusions. Random measurement error is therefore analyzed there rather than in the title, procedure, or references.

Question 18Scientific Inquiry and the Processes of Chemistry

A student must prepare exactly 250.0 mL of a 0.100 M aqueous solution from a concentrated stock. Which piece of glassware is designed for this final volume measurement?

  1. A 250-mL Erlenmeyer flask
  2. A 250-mL graduated cylinder
  3. A 250-mL volumetric flask Correct answer.
  4. A 250-mL beaker

Explanation

A volumetric flask has a single calibration mark and a long neck, so it is designed to contain a precise final volume when filled to the mark. Beakers, Erlenmeyer flasks, and graduated cylinders are not intended for precise final-volume preparation.

Question 19Scientific Inquiry and the Processes of Chemistry

A student standardizes a NaOH solution and calculates its concentration as 0.1012 M, but the true concentration is 0.0998 M. The student then uses the calculated concentration to titrate an acid sample. How will the reported acid concentration be affected, assuming all other measurements are accurate?

  1. Too high, because an inflated NaOH molarity overestimates base moles Correct answer.
  2. Too low, because the assumed NaOH concentration is larger than the true value
  3. Unaffected, because the same volume of NaOH is delivered
  4. Unaffected, because the error is random rather than systematic

Explanation

Using 0.1012 M instead of 0.0998 M makes the student calculate more moles of NaOH delivered than were actually present. That overestimates the moles of acid neutralized, so the reported acid concentration is too high.

Question 20Scientific Inquiry and the Processes of Chemistry

A student determines the percent water in a hydrate by heating the sample to constant mass. If the sample is not heated to constant mass and some water remains, how will the calculated percent water compare with the true value?

  1. It will be unchanged, because only the final mass matters
  2. It will be higher than the true value
  3. It will be lower than the true value Correct answer.
  4. It will be higher or lower depending on the crucible mass

Explanation

Percent water is calculated from the mass lost during heating. If some water remains, the measured mass loss is smaller than the true water mass, so the calculated percent water is lower than the true value.

Question 21Scientific Inquiry and the Processes of Chemistry

Which statement best describes the relationship between a scientific theory and a scientific law in chemistry?

  1. A theory becomes a law once it has been tested by enough experiments.
  2. A law explains the mechanism of a phenomenon, whereas a theory describes only what happens.
  3. A theory explains observations; a law summarizes a consistent measurable relationship. Correct answer.
  4. A theory is a tentative guess, whereas a law is a proven fact that cannot be revised.

Explanation

A scientific theory is an evidence-supported explanatory framework for why observations occur, while a scientific law is a concise statement of a regularity, often expressed mathematically. Theories do not turn into laws as they gain support, and both remain open to revision if new evidence requires it.

Question 22Scientific Inquiry and the Processes of Chemistry

A student measures the volume of a liquid in a graduated cylinder whose smallest markings are 1 mL. Which recorded value correctly reflects the precision normally expected for this instrument?

  1. 18.0 mL Correct answer.
  2. 18.00 mL
  3. 18.000 mL
  4. 18 mL

Explanation

When the smallest markings are 1 mL, the student should estimate one digit beyond the markings, giving a reading to the nearest 0.1 mL. Recording 18.0 mL reflects that estimated precision, while more decimal places imply an unjustified level of certainty.

Question 23Scientific Inquiry and the Processes of Chemistry

A small amount of dilute hydrochloric acid splashes into a student's eye during a laboratory period. Which action should the student take first?

  1. Flush the eye at the eyewash station with water for at least 15 minutes. Correct answer.
  2. Apply an antibiotic eye drop and continue the experiment.
  3. Neutralize the eye with dilute sodium bicarbonate solution.
  4. Rub the eye gently and then notify the instructor at the end of the period.

Explanation

Immediate and prolonged flushing with water at an eyewash station is the standard first response for chemical exposure to the eyes. Medical attention and notification of the instructor should follow, but flushing must begin without delay.

Question 24Scientific Inquiry and the Processes of Chemistry

A student performing replicate acid-base titrations obtains the following volumes of titrant: 12.05 mL, 12.07 mL, 12.06 mL, and 15.22 mL. What is the most appropriate next step in processing these data?

  1. Check the 15.22 mL trial for a documented procedural error. Correct answer.
  2. Discard the 15.22 mL trial and report the mean of the other three volumes.
  3. Average all four values because every measurement must be included.
  4. Report the median of all four values as the final result without comment.

Explanation

An apparent outlier should not be discarded automatically; the student should first inspect the trial for a known problem such as an overshot endpoint or a misread burette. If a documented error is found, exclusion may be justified, but otherwise the value should be retained or evaluated statistically.

Question 25Scientific Inquiry and the Processes of Chemistry

A student plots mass on the y-axis versus volume on the x-axis for several samples of an unknown metal and obtains a straight line. What does the slope of this graph represent?

  1. The density of the metal Correct answer.
  2. The reciprocal of the metal's density
  3. The specific heat capacity of the metal
  4. The molar mass of the metal

Explanation

The slope equals the change in mass divided by the change in volume, which has units such as g/mL or g/cm³. That ratio is the density of the metal, not its molar mass or heat capacity.

Question 26Scientific Inquiry and the Processes of Chemistry

In a spectrophotometric determination of copper(II) ion concentration, why is a blank sample measured before the standard solutions?

  1. To determine the wavelength of maximum absorbance for the copper(II) complex.
  2. To precipitate any interfering ions before the standards are measured.
  3. To set the instrument's zero absorbance with solvent and reagents but no analyte. Correct answer.
  4. To calculate the path length of the cuvette from the blank's absorbance.

Explanation

The blank contains the same solvent and reagents as the standards but omits the analyte, so it establishes the zero-absorbance reference and corrects for background absorption. Wavelength selection and cuvette path length are handled separately.

Question 27Scientific Inquiry and the Processes of Chemistry

A volumetric flask is marked 'TC 25 °C.' What does this marking indicate about the flask?

  1. It contains its stated volume when filled to the mark at 25 °C. Correct answer.
  2. It may be heated safely to 25 °C above room temperature.
  3. It is calibrated to deliver its stated volume by gravity at 25 °C.
  4. It must be stored at exactly 25 °C to maintain its calibration.

Explanation

The abbreviation TC means 'to contain,' so the flask holds its stated volume when filled to the calibration mark at 25 °C. By contrast, TD means 'to deliver,' which is typical of pipettes and burettes.

Question 28Scientific Inquiry and the Processes of Chemistry

A well-supported chemical theory predicts a product distribution that is contradicted by a carefully repeated, high-quality experiment. What is the most scientifically appropriate response?

  1. Reclassify the theory as a law so that it no longer needs to agree with data.
  2. Repeat the experiment and examine whether the theory's assumptions or scope need revision. Correct answer.
  3. Ignore the new result because the theory has already been accepted.
  4. Reject the theory immediately and replace it with the first alternative proposed.

Explanation

Scientific theories are robust but provisional, so an anomalous result should prompt replication and careful review of the theory's assumptions or scope. A single contradiction does not justify immediate replacement, and ignoring data is never appropriate.

Question 29Scientific Inquiry and the Processes of Chemistry

A student uses the ideal gas law to calculate the moles of a gas sample from measurements made near the gas's boiling point at high pressure. Which factor most likely causes the calculated value to deviate from the actual moles?

  1. The gas constant depends on the pressure of the sample.
  2. The ideal gas law is valid only at absolute zero.
  3. Real gases have nonzero particle volume and intermolecular attractions. Correct answer.
  4. Kelvin temperatures cannot be used in gas-law calculations.

Explanation

Near condensation and at high pressure, gas particles are close together, so finite particle volume and intermolecular attractions become significant. The ideal gas model assumes these effects are negligible, so its predictions deviate from real behavior under such conditions.

Question 30Scientific Inquiry and the Processes of Chemistry

A student's calibration curve for lead(II) ion concentration is linear from 0 to 5.0 mg/L with R² = 0.998. A sample's absorbance falls above the highest standard, and dilution brings it into the calibrated range. What is the most important reason to dilute rather than extrapolate the curve?

  1. Absorbance measurements are valid only for samples with pH below 7.
  2. Dilution eliminates all possible matrix interferences in the sample.
  3. The R² value guarantees that the slope is constant at any concentration.
  4. Extrapolation assumes linearity beyond the validated range of standards. Correct answer.

Explanation

A calibration curve is validated only over the concentration range of its standards, so extrapolating beyond that range assumes the same response continues when detector nonlinearity or chemistry changes may occur. Diluting the sample brings it into the validated range and reduces that risk.

Question 31Scientific Inquiry and the Processes of Chemistry

A chemist proposes that increasing the concentration of permanganate ion will increase the rate of its reaction with oxalic acid. Which statement best describes the role of this proposal in the investigation?

  1. It is a scientific law because it predicts the direction in which the reaction rate will change.
  2. It is a testable hypothesis that can be evaluated by measuring reaction rate at several permanganate concentrations. Correct answer.
  3. It is an observation because permanganate concentration can be measured directly.
  4. It is a scientific theory because it explains why permanganate reacts with oxalic acid.

Explanation

A hypothesis is a tentative, testable explanation or prediction that can be evaluated with controlled experiments. Here, varying permanganate concentration and measuring reaction rate would directly test the proposed relationship. A law summarizes observed regularity, while a theory is a broader explanatory framework supported by extensive evidence.

Question 32Scientific Inquiry and the Processes of Chemistry

A student calculates the density of a metal sample by dividing a mass of 12.30 g by a volume of 3.5 mL. Which reported density correctly reflects the significant figures of these measurements?

  1. 3.514 g/mL
  2. 4.0 g/mL
  3. 3.5 g/mL Correct answer.
  4. 3.51 g/mL

Explanation

For multiplication and division, the result is limited by the measurement with the fewest significant figures. The volume 3.5 mL has two significant figures, so the quotient 12.30 g ÷ 3.5 mL must be reported to two significant figures. The correctly rounded density is therefore 3.5 g/mL.

Question 33Scientific Inquiry and the Processes of Chemistry

A student rinses a burette with distilled water instead of the standardized NaOH titrant before filling it. The water remaining in the burette dilutes the titrant during a titration of an acid sample. Assuming all other measurements are accurate, what is the effect on the calculated acid concentration?

  1. A systematic error that makes the calculated acid concentration too high Correct answer.
  2. A random error that makes the calculated acid concentration too low
  3. A systematic error that makes the calculated acid concentration too low
  4. A random error that affects precision but not the average calculated concentration

Explanation

Residual water dilutes the NaOH, so the actual titrant concentration is lower than the standardized value used in calculations. More titrant volume is needed to reach the endpoint, and using the higher assumed concentration with this larger volume overestimates the moles of base delivered. The resulting calculated acid concentration is systematically too high.

Question 34Scientific Inquiry and the Processes of Chemistry

A student has a small volume of dilute aqueous copper(II) sulfate left after an experiment. Which action is most appropriate for disposing of this waste?

  1. Pour it down the sink because it is dilute and water-soluble.
  2. Place it in a labeled heavy-metal waste container according to the institution's waste procedures. Correct answer.
  3. Neutralize it with strong acid and then pour it down the sink.
  4. Evaporate it to dryness on the laboratory bench and discard the solid in the trash.

Explanation

Copper(II) sulfate contains a heavy-metal ion and should not be discharged to the sink under typical school laboratory rules. Chemical waste must be segregated and labeled according to the institution's hazardous-waste procedures. Dilution, evaporation, or acid neutralization does not make heavy-metal waste suitable for ordinary disposal.

Question 35Atomic Structure and the Periodic Table

What is the maximum number of electrons that can occupy the n = 3 principal energy level of an atom?

  1. 10
  2. 18 Correct answer.
  3. 32
  4. 8

Explanation

The n = 3 level contains one 3s orbital, three 3p orbitals, and five 3d orbitals. Each orbital holds two electrons, so the capacity is 2 + 6 + 10 = 18 electrons. The value 8 applies to n = 2, and 32 applies to n = 4.

Question 36Atomic Structure and the Periodic Table

Which of the following alkali metals has the smallest atomic radius?

  1. Lithium (Li) Correct answer.
  2. Potassium (K)
  3. Sodium (Na)
  4. Rubidium (Rb)

Explanation

Atomic radius increases down a group as additional principal shells are added. Lithium is at the top of Group 1 and has only the n = 2 valence shell, so it is the smallest of these alkali metals. Rubidium, near the bottom of the group, is the largest.

Question 37Atomic Structure and the Periodic Table

How many neutrons are present in the nucleus of a sulfur-34 atom (³⁴S)?

  1. 34
  2. 16
  3. 18 Correct answer.
  4. 32

Explanation

The mass number 34 equals the sum of protons and neutrons, and sulfur's atomic number is 16. Subtracting the 16 protons from 34 gives 18 neutrons. The numbers 16 and 34 refer to protons and mass number, respectively.

Question 38Atomic Structure and the Periodic Table

Which ground-state electron configuration is correct for a chromium atom (Z = 24)?

  1. [Ar] 3d⁵ 4s¹ Correct answer.
  2. [Ar] 3d⁶
  3. [Ar] 3d⁴ 4s²
  4. [Ar] 4s² 3d⁴

Explanation

Chromium is a recognized exception to the straightforward Aufbau filling order. A half-filled 3d⁵ set with a single 4s electron is lower in energy than 3d⁴4s², so the ground state is [Ar]3d⁵4s¹. The configuration [Ar]3d⁴4s² is the naive prediction but not the observed ground state.

Question 39Atomic Structure and the Periodic Table

An element has the ground-state electron configuration [Kr] 5s² 4d¹⁰ 5p³. In which group of the periodic table does this element belong?

  1. Group 15 Correct answer.
  2. Group 13
  3. Group 17
  4. Group 5

Explanation

The valence configuration is 5s²5p³, giving five valence electrons. Elements with five valence electrons occupy Group 15 of the periodic table. The filled 4d¹⁰ subshell lies below the valence shell and does not change the group assignment.

Question 40Atomic Structure and the Periodic Table

Which element has a second ionization energy that is unusually high compared with its first ionization energy?

  1. Magnesium (Mg)
  2. Sodium (Na) Correct answer.
  3. Silicon (Si)
  4. Aluminum (Al)

Explanation

Sodium's first ionization removes its single 3s electron, leaving the stable neon-like 2p⁶ core. Removing a second electron therefore requires breaking into a closed shell, causing a very large jump. For magnesium and aluminum, the second electron comes from the valence region, so the increase is less dramatic.

Question 41Atomic Structure and the Periodic Table

Across Period 3 from sodium to chlorine, the atomic radius decreases primarily because:

  1. effective nuclear charge increases Correct answer.
  2. the neutron-to-proton ratio increases
  3. valence-electron repulsion increases
  4. the number of occupied electron shells increases

Explanation

Across a period, protons are added to the nucleus while electrons enter the same principal shell. The added nuclear charge is not fully shielded by the increasing valence electron count, so the effective nuclear charge rises and pulls the valence shell inward. The number of shells does not increase across the period.

Question 42Atomic Structure and the Periodic Table

How many unpaired electrons are in the ground-state electron configuration of Fe²⁺ (Z = 26)?

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

Explanation

Neutral iron is [Ar]3d⁶4s², so Fe²⁺ loses the two 4s electrons and becomes [Ar]3d⁶. In a high-spin d⁶ configuration, one d orbital is doubly occupied and four are singly occupied, giving four unpaired electrons. Pairing all six would give only two unpaired and is not the ground-state Hund arrangement.

Question 43Atomic Structure and the Periodic Table

The atomic radius of gallium (135 pm) is nearly the same as that of aluminum (143 pm) even though gallium lies below aluminum in Group 13. Which explanation best accounts for this observation?

  1. Ga's 4p electrons penetrate the nucleus more than Al's 3p electrons.
  2. Poor 3d shielding contracts Ga's outer orbitals. Correct answer.
  3. Ga has fewer occupied principal energy levels than Al.
  4. Ga has more neutrons, raising its effective nuclear charge.

Explanation

The filled 3d¹⁰ subshell in gallium shields the nuclear charge poorly. As a result, the effective nuclear charge felt by Ga's 4s and 4p electrons is larger than a simple shell-count argument predicts, contracting the atom. This d-block contraction offsets the usual increase in radius down a group.

Question 44Atomic Structure and the Periodic Table

Which pair of elements would be expected to have the most similar chemical properties?

  1. Na and Mg
  2. Mg and Ca Correct answer.
  3. C and N
  4. Fe and Co

Explanation

Magnesium and calcium both lie in Group 2 and share the valence configuration ns². Elements in the same group tend to show similar chemical behavior because they have the same number and type of valence electrons. The other pairs cross group boundaries or are not in the same group.

Question 45Atomic Structure and the Periodic Table

Which set of quantum numbers (n, ℓ, mℓ, ms) is allowed for an electron in a 3d subshell?

  1. (3, 1, 0, +1/2)
  2. (3, 2, −1, +1/2) Correct answer.
  3. (3, 2, +3, −1/2)
  4. (2, 2, 0, −1/2)

Explanation

For a 3d subshell, the principal quantum number must be n = 3 and the angular momentum quantum number must be ℓ = 2. The magnetic quantum number mℓ may range from −2 to +2, and the spin quantum number ms may be +1/2 or −1/2. Only the set (3, 2, −1, +1/2) satisfies all of these conditions.

Question 46Atomic Structure and the Periodic Table

Chlorine-35 and chlorine-37 are two isotopes of chlorine. Which statement about these nuclides is correct?

  1. They contain equal mass numbers but unequal protons.
  2. They contain unequal protons and unequal neutrons.
  3. They contain equal numbers of neutrons.
  4. They contain equal protons but unequal neutrons. Correct answer.

Explanation

Isotopes of an element have the same atomic number, meaning the same number of protons, but different mass numbers because they have different numbers of neutrons. Chlorine-35 contains 18 neutrons, while chlorine-37 contains 20 neutrons.

Question 47Atomic Structure and the Periodic Table

Which group of the periodic table contains elements whose neutral atoms have a filled valence p subshell?

  1. Group 17
  2. Group 15
  3. Group 18 Correct answer.
  4. Group 1

Explanation

Group 18 elements, the noble gases, have a filled valence p subshell in their ground-state configurations (ns² np⁶), except helium, whose 1s subshell is full. Groups 1, 15, and 17 have partially filled valence subshells.

Question 48Atomic Structure and the Periodic Table

Which Period 3 element has the most negative (largest-magnitude) first electron affinity?

  1. Sodium
  2. Chlorine Correct answer.
  3. Silicon
  4. Argon

Explanation

Across Period 3, effective nuclear charge increases while the added electrons enter the same principal shell, so electron affinity generally becomes more negative. Chlorine has the most negative first electron affinity in Period 3, while argon has a stable octet and essentially no tendency to accept an electron.

Question 49Atomic Structure and the Periodic Table

The first ionization energy of magnesium is greater than that of sodium. Which factor primarily accounts for this difference?

  1. Mg has a higher effective nuclear charge on the 3s electron. Correct answer.
  2. Mg removes a 3p electron, which lies closer to the nucleus than 3s.
  3. Mg has an extra filled inner shell that shields the 3s electron more.
  4. Mg has a larger atomic radius, so its 3s electron is less tightly held.

Explanation

Both sodium and magnesium lose an electron from the 3s orbital, and their inner shells shield the nucleus similarly. Magnesium has one additional proton, so the effective nuclear charge felt by the 3s electron is greater, which raises the first ionization energy.

Question 50Atomic Structure and the Periodic Table

What is the ground-state electron configuration of the Co³⁺ ion (Z = 27)?

  1. [Ar] 3d⁸
  2. [Ar] 4s² 3d⁴
  3. [Ar] 3d⁵ 4s¹
  4. [Ar] 3d⁶ Correct answer.

Explanation

Neutral cobalt has the configuration [Ar] 4s² 3d⁷. For transition-metal cations, electrons are removed from the highest principal shell first, so the two 4s electrons are lost before 3d electrons. Removing three electrons from Co therefore gives [Ar] 3d⁶.