I85PREP
⌘ K
DAT Natural Sciences study materials
DAT Natural Sciences study resources

DAT Natural Sciences practice questions

One question at a time. Build your DAT Natural Sciences understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Survey of the Natural Sciences

Which cellular organelle is the primary site of ATP synthesis by oxidative phosphorylation in a eukaryotic cell?

  1. Smooth endoplasmic reticulum
  2. Lysosome
  3. Golgi apparatus
  4. Mitochondrion Correct answer.

Explanation

The inner mitochondrial membrane houses the electron transport chain and ATP synthase, which together carry out oxidative phosphorylation. The proton gradient across that membrane drives ATP production. Other organelles listed perform unrelated roles in sorting, degradation, or lipid synthesis.

Question 2Survey of the Natural Sciences

During which phase of mitosis do sister chromatids separate and move toward opposite poles of the cell?

  1. Metaphase
  2. Anaphase Correct answer.
  3. Prophase
  4. Telophase

Explanation

Anaphase begins when cohesin is cleaved and sister chromatids are pulled apart by shortening kinetochore microtubules. This poleward movement defines anaphase. Prophase and metaphase precede separation, and telophase follows it during nuclear envelope reformation.

Question 3Survey of the Natural Sciences

A mutation changes a codon from UAU to UAA in the middle of an mRNA coding sequence. What is the most likely consequence for the resulting polypeptide?

  1. A single amino acid substitution with no effect on length
  2. Duplication of the entire polypeptide chain
  3. Premature termination of translation Correct answer.
  4. A frameshift altering every downstream codon

Explanation

UAA is one of the three stop codons, so the ribosome will release the nascent chain when it reaches this position. The result is a truncated polypeptide rather than a full-length protein. Frameshifts require insertions or deletions that are not multiples of three, which is not the case here.

Question 4Survey of the Natural Sciences

In a population at Hardy-Weinberg equilibrium, the frequency of the recessive allele is 0.3. What proportion of the population is expected to be heterozygous?

  1. 0.49
  2. 0.21
  3. 0.42 Correct answer.
  4. 0.09

Explanation

Heterozygote frequency is 2pq. With q = 0.3, p = 0.7, so 2pq = 2(0.7)(0.3) = 0.42. The value 0.09 corresponds to q squared and 0.49 to p squared.

Question 5Survey of the Natural Sciences

Which blood vessel carries oxygenated blood from the lungs to the heart?

  1. Pulmonary artery
  2. Pulmonary vein Correct answer.
  3. Aorta
  4. Superior vena cava

Explanation

The pulmonary veins return oxygenated blood from the lungs to the left atrium. This is the standard exception to the rule that veins carry deoxygenated blood. The pulmonary artery carries deoxygenated blood away from the heart toward the lungs.

Question 6Survey of the Natural Sciences

A patient's blood pH is measured at 7.30 with elevated CO2 and normal bicarbonate. Which acid-base disturbance is most consistent with these values?

  1. Respiratory alkalosis
  2. Metabolic acidosis
  3. Metabolic alkalosis
  4. Respiratory acidosis Correct answer.

Explanation

Elevated CO2 with a low pH indicates retention of carbon dioxide, which is a respiratory acidosis. Normal bicarbonate suggests the disturbance is not primarily metabolic. Compensation would later raise bicarbonate if the condition persisted.

Question 7Survey of the Natural Sciences

Which structure of the nephron is primarily responsible for the reabsorption of the majority of filtered water and solutes?

  1. Collecting duct
  2. Glomerulus
  3. Proximal convoluted tubule Correct answer.
  4. Descending limb of the loop of Henle

Explanation

The proximal convoluted tubule reabsorbs roughly two-thirds of filtered water and sodium, aided by abundant microvilli and mitochondria. It is the principal site of bulk reabsorption. Later segments fine-tune water and electrolyte balance under hormonal control.

Question 8Survey of the Natural Sciences

A block slides down a frictionless incline of height 5 m. If it starts from rest, what is its speed at the bottom? Use g = 10 m/s².

  1. 14 m/s
  2. 10 m/s Correct answer.
  3. 5 m/s
  4. 20 m/s

Explanation

Conservation of energy gives mgh = ½mv², so v = √(2gh) = √(2 × 10 × 5) = √100 = 10 m/s. The mass cancels, so the result is independent of the block's mass. Frictionless conditions mean no energy is lost to heat.

Question 9Survey of the Natural Sciences

Which of the following best describes the direction of the magnetic force on a positively charged particle moving parallel to a uniform magnetic field?

  1. Perpendicular to both velocity and field
  2. Zero, because the velocity is parallel to the field Correct answer.
  3. Opposite to the magnetic field
  4. Parallel to the velocity

Explanation

The magnetic force is given by F = qv × B. When velocity and field are parallel, the cross product is zero, so no magnetic force acts on the particle. Maximum force occurs when velocity is perpendicular to the field.

Question 10Survey of the Natural Sciences

An object is placed 30 cm from a converging lens with a focal length of 10 cm. Where is the image formed?

  1. 10 cm on the same side as the object
  2. 30 cm on the opposite side of the lens
  3. 15 cm on the opposite side of the lens Correct answer.
  4. 60 cm on the same side as the object

Explanation

Using 1/f = 1/do + 1/di gives 1/10 = 1/30 + 1/di, so 1/di = 1/10 − 1/30 = 2/30, and di = 15 cm. A positive image distance places the image on the opposite side, where it is real and inverted.

Question 11Survey of the Natural Sciences

Which intermolecular force is primarily responsible for the unusually high boiling point of water compared with hydrogen sulfide?

  1. Ion-dipole interactions
  2. London dispersion forces
  3. Hydrogen bonding Correct answer.
  4. Dipole-dipole interactions

Explanation

Water forms extensive hydrogen bonds because oxygen is highly electronegative and bears lone pairs. These stronger interactions require more energy to overcome, raising the boiling point. Hydrogen sulfide has weaker hydrogen bonding because sulfur is less electronegative.

Question 12Survey of the Natural Sciences

How many moles of oxygen gas are required to completely combust 2 moles of methane according to CH4 + 2O2 → CO2 + 2H2O?

  1. 2 moles
  2. 4 moles Correct answer.
  3. 1 mole
  4. 3 moles

Explanation

The balanced equation shows a 1:2 ratio of methane to oxygen, so 2 moles of methane require 4 moles of oxygen. Stoichiometric coefficients give the molar ratio directly. This assumes complete combustion to CO2 and water.

Question 13Survey of the Natural Sciences

Which of the following solutions would have the lowest pH?

  1. 0.1 M NaOH
  2. 0.1 M NaCl
  3. 0.1 M HCl Correct answer.
  4. 0.1 M acetic acid

Explanation

HCl is a strong acid that dissociates completely, giving a hydrogen ion concentration of 0.1 M and a pH of 1. Acetic acid is weak and only partially dissociates, giving a higher pH. NaOH is basic and NaCl is neutral.

Question 14Survey of the Natural Sciences

In a galvanic cell, oxidation occurs at which electrode, and what is the sign of that electrode?

  1. Cathode, positive
  2. Anode, negative Correct answer.
  3. Anode, positive
  4. Cathode, negative

Explanation

In a galvanic cell, oxidation takes place at the anode, which is the negative electrode because electrons are released there. Reduction occurs at the cathode, which is positive. This convention is the opposite of an electrolytic cell's labeling.

Question 15Survey of the Natural Sciences

Which of the following describes the hybridization of carbon in a molecule of ethene (C2H4)?

  1. sp
  2. sp2 Correct answer.
  3. sp3d
  4. sp3

Explanation

Each carbon in ethene forms three sigma bonds and one pi bond, requiring three hybrid orbitals and thus sp2 hybridization. The remaining unhybridized p orbital forms the pi bond. The geometry around each carbon is trigonal planar.

Question 16Survey of the Natural Sciences

Which functional group is present in a molecule that reacts with Tollens' reagent to form a silver mirror?

  1. Aldehyde Correct answer.
  2. Tertiary alcohol
  3. Ketone
  4. Ether

Explanation

Tollens' reagent oxidizes aldehydes to carboxylates while reducing silver ions to metallic silver, producing a mirror. Ketones lack the reactive hydrogen needed for this oxidation. The test distinguishes aldehydes from most other carbonyl compounds.

Question 17Survey of the Natural Sciences

Which of the following is the correct IUPAC name for the compound CH3-CH2-CH2-OH?

  1. Propan-1-ol Correct answer.
  2. Propanal
  3. Propan-2-ol
  4. Propanoic acid

Explanation

The three-carbon chain with a hydroxyl group on the terminal carbon is propan-1-ol. The suffix -ol indicates an alcohol. Propan-2-ol would place the hydroxyl on the middle carbon.

Question 18Survey of the Natural Sciences

A reaction has a ΔG° of +20 kJ/mol at 298 K. Which statement correctly describes the reaction under standard conditions?

  1. It is spontaneous only at high temperature
  2. It is nonspontaneous and has K < 1 Correct answer.
  3. It is spontaneous and has K > 1
  4. It is at equilibrium with K = 1

Explanation

A positive ΔG° indicates a nonspontaneous reaction under standard conditions, corresponding to an equilibrium constant less than one because ΔG° = −RT ln K. The reaction may proceed in reverse spontaneously. Spontaneity depends on temperature only insofar as ΔG itself varies with T.

Question 19Survey of the Natural Sciences

Which of the following best explains why a buffer resists pH change upon addition of a small amount of strong acid?

  1. The conjugate base in the buffer neutralizes added H+ Correct answer.
  2. The acid is diluted by the buffer solution
  3. The buffer raises the temperature to evaporate the acid
  4. The strong acid precipitates out of solution

Explanation

A buffer contains a weak acid and its conjugate base. Added H+ is consumed by the conjugate base, forming more weak acid and limiting the pH drop. This equilibrium shift is the basis of buffer action.

Question 20Survey of the Natural Sciences

Which of the following is the correct order of increasing electronegativity?

  1. Cl < P < Si < Na
  2. Si < Na < Cl < P
  3. Na < Si < P < Cl Correct answer.
  4. Na < P < Si < Cl

Explanation

Electronegativity increases across a period from left to right. Sodium is a metal with low electronegativity, while chlorine is a highly electronegative halogen. The order Na < Si < P < Cl reflects that trend.

Question 21Survey of the Natural Sciences

A dihybrid cross between two heterozygous individuals (AaBb × AaBb) with independent assortment produces offspring. What fraction is expected to show both recessive phenotypes?

  1. 9/16
  2. 3/16
  3. 1/4
  4. 1/16 Correct answer.

Explanation

Each trait shows a 1/4 probability of the recessive phenotype. Multiplying independent probabilities gives 1/4 × 1/4 = 1/16 for both recessive phenotypes. This reflects the 9:3:3:1 phenotypic ratio.

Question 22Survey of the Natural Sciences

Which of the following best describes the role of the sodium-potassium pump in maintaining the resting membrane potential of a neuron?

  1. It moves three K+ out and two Na+ in, making the interior positive
  2. It allows both ions to diffuse freely down their gradients
  3. It transports chloride ions into the cell to hyperpolarize it
  4. It moves three Na+ out and two K+ in, contributing to a negative interior Correct answer.

Explanation

The pump exports three sodium ions and imports two potassium ions per ATP hydrolyzed. This net loss of positive charge contributes to the negative resting potential. The pump also maintains the concentration gradients that drive later action potentials.

Question 23Survey of the Natural Sciences

A woman who is a carrier for an X-linked recessive disorder has children with an unaffected man. What proportion of their sons is expected to be affected?

  1. 1/4
  2. 0
  3. All sons
  4. 1/2 Correct answer.

Explanation

Sons inherit their single X chromosome from the mother. A carrier mother transmits the mutant allele to half of her sons, who then express the recessive disorder because they have no second X. Daughters are unaffected or carriers depending on which paternal X they inherit.

Question 24Survey of the Natural Sciences

An enzyme-catalyzed reaction shows a decreased Vmax but an unchanged Km when a reversible inhibitor is added. Which type of inhibition does this describe?

  1. Uncompetitive inhibition
  2. Competitive inhibition
  3. Noncompetitive inhibition Correct answer.
  4. Irreversible inhibition

Explanation

Noncompetitive inhibitors bind at a site other than the active site and reduce Vmax without altering Km because substrate binding affinity is unchanged. Competitive inhibitors raise Km while leaving Vmax unchanged. Uncompetitive inhibitors lower both Vmax and Km.

Question 25Survey of the Natural Sciences

In a species of flowering plant, red flower color (R) is incompletely dominant over white (r), with heterozygotes showing pink flowers. If two pink-flowered plants are crossed, what phenotypic ratio is expected among the offspring?

  1. 3 red : 1 white
  2. All pink
  3. 1 red : 1 white
  4. 1 red : 2 pink : 1 white Correct answer.

Explanation

Incomplete dominance produces a distinct heterozygote phenotype. Crossing Rr × Rr yields 1 RR (red) : 2 Rr (pink) : 1 rr (white). The heterozygous phenotype is intermediate rather than dominant.

Question 26Survey of the Natural Sciences

Which of the following best describes the primary function of the loop of Henle in the nephron?

  1. Filtration of blood plasma
  2. Reabsorption of glucose and amino acids
  3. Establishment of a medullary osmotic gradient Correct answer.
  4. Secretion of hydrogen ions

Explanation

The loop of Henle creates a concentration gradient in the renal medulla through countercurrent multiplication, which is essential for concentrating urine. This gradient allows water reabsorption from the collecting duct under the influence of ADH.

Question 27Survey of the Natural Sciences

A 2 kg block is lifted vertically at a constant speed of 3 m/s. What is the power delivered by the lifting force? (Use g = 10 m/s².)

  1. 30 W
  2. 60 W Correct answer.
  3. 20 W
  4. 6 W

Explanation

Power equals force multiplied by velocity. The lifting force must equal the weight, mg = 2 kg × 10 m/s² = 20 N, so power = 20 N × 3 m/s = 60 W. Constant speed means no net force, so the applied force exactly balances gravity.

Question 28Survey of the Natural Sciences

A positively charged particle enters a uniform magnetic field directed into the page with a velocity pointing to the right. What is the direction of the magnetic force on the particle?

  1. Upward Correct answer.
  2. Downward
  3. Into the page
  4. Out of the page

Explanation

Using the right-hand rule for a positive charge: velocity to the right, magnetic field into the page, the force is perpendicular to both and points upward. The magnetic force is always perpendicular to the velocity and the field.

Question 29Survey of the Natural Sciences

Which of the following correctly describes the image formed by a plane mirror?

  1. Real, inverted, and smaller than the object
  2. Virtual, inverted, and larger than the object
  3. Real, upright, and the same size as the object
  4. Virtual, upright, and the same size as the object Correct answer.

Explanation

A plane mirror always forms a virtual image that is upright and the same size as the object, located as far behind the mirror as the object is in front. The image cannot be projected onto a screen because the light rays do not actually converge.

Question 30Survey of the Natural Sciences

Which of the following molecules has a net dipole moment?

  1. CO2
  2. CCl4
  3. BF3
  4. H2O Correct answer.

Explanation

Water has a bent geometry, so its polar O–H bonds do not cancel and the molecule has a net dipole. In contrast, CO2, CCl4, and BF3 are highly symmetric, causing their bond dipoles to cancel.

Question 31Survey of the Natural Sciences

Which of the following is the conjugate base of H2PO4⁻?

  1. H3PO4
  2. H2PO4
  3. HPO4²⁻ Correct answer.
  4. PO4³⁻

Explanation

The conjugate base is formed by removing one proton (H⁺) from the acid. Removing H⁺ from H2PO4⁻ gives HPO4²⁻, so that is the conjugate base.

Question 32Survey of the Natural Sciences

Which of the following best describes the mechanism of action of a competitive inhibitor?

  1. It binds irreversibly to the enzyme and permanently inactivates it.
  2. It binds to the enzyme-substrate complex and prevents product release.
  3. It binds to the active site and increases the apparent Km. Correct answer.
  4. It binds to an allosteric site and decreases Vmax.

Explanation

A competitive inhibitor structurally resembles the substrate and binds reversibly to the active site, competing with substrate. This increases the apparent Km because more substrate is needed to reach half-maximal velocity, but Vmax can still be reached at high substrate concentration.

Question 33Survey of the Natural Sciences

In a population at Hardy-Weinberg equilibrium, the frequency of the recessive allele is 0.2. What is the frequency of heterozygous individuals?

  1. 0.64
  2. 0.16
  3. 0.32 Correct answer.
  4. 0.04

Explanation

If q = 0.2, then p = 0.8. The heterozygous frequency is 2pq = 2 × 0.8 × 0.2 = 0.32. This assumes random mating and no evolutionary forces acting on the locus.

Question 34Survey of the Natural Sciences

Which of the following is the correct sequence of events during the cardiac cycle?

  1. Atrial systole, ventricular ejection, isovolumetric ventricular contraction, isovolumetric relaxation
  2. Isovolumetric ventricular contraction, atrial systole, ventricular ejection, isovolumetric relaxation
  3. Atrial systole, isovolumetric ventricular contraction, ventricular ejection, isovolumetric relaxation Correct answer.
  4. Ventricular ejection, atrial systole, isovolumetric relaxation, isovolumetric ventricular contraction

Explanation

The cardiac cycle begins with atrial systole, followed by isovolumetric ventricular contraction when all valves are closed, then ventricular ejection when semilunar valves open, and finally isovolumetric relaxation when all valves are closed again. This sequence ensures efficient blood flow.

Question 35Survey of the Natural Sciences

A 5 kg block is pushed across a horizontal surface with a constant force of 20 N. If the coefficient of kinetic friction is 0.2, what is the acceleration of the block? (Use g = 10 m/s².)

  1. 0.4 m/s²
  2. 6 m/s²
  3. 4 m/s²
  4. 2 m/s² Correct answer.

Explanation

The frictional force is μk × N = 0.2 × (5 kg × 10 m/s²) = 10 N. The net force is 20 N − 10 N = 10 N, so acceleration = Fnet/m = 10 N / 5 kg = 2 m/s².

Question 36Survey of the Natural Sciences

A solution contains 0.10 M acetic acid (Ka = 1.8 × 10⁻⁵) and 0.10 M sodium acetate. What is the pH of the solution?

  1. 2.87
  2. 7.00
  3. 9.26
  4. 4.74 Correct answer.

Explanation

Using the Henderson-Hasselbalch equation, pH = pKa + log([A⁻]/[HA]). Since [A⁻] = [HA], pH = pKa = −log(1.8 × 10⁻⁵) ≈ 4.74.

Question 37Survey of the Natural Sciences

Which of the following statements about a spontaneous electrochemical reaction is always true?

  1. The cell potential is positive and ΔG is negative. Correct answer.
  2. The cell potential is negative and ΔG is positive.
  3. The cell potential is positive and ΔG is positive.
  4. The cell potential is negative and ΔG is negative.

Explanation

For a spontaneous reaction, the change in Gibbs free energy (ΔG) must be negative. In an electrochemical cell, ΔG = −nFE, so a positive cell potential (E) corresponds to a negative ΔG.

Question 38Survey of the Natural Sciences

Which of the following compounds is aromatic?

  1. Cyclohexane
  2. Cyclooctatetraene
  3. 1,3-Cyclohexadiene
  4. Benzene Correct answer.

Explanation

Benzene is planar, cyclic, fully conjugated, and has 6 π electrons (4n+2 with n=1), satisfying Hückel's rule. The other options lack one or more of these criteria.

Question 39Survey of the Natural Sciences

In a cross between two individuals heterozygous for a recessive lethal allele (Aa × Aa), what is the expected phenotypic ratio among the surviving offspring?

  1. 1:1
  2. 3:1
  3. 1:2:1
  4. 2:1 Correct answer.

Explanation

The genotypes at conception are 1 AA : 2 Aa : 1 aa. If aa is lethal, the surviving offspring are 1 AA : 2 Aa, giving a phenotypic ratio of 2:1 (assuming complete dominance).

Question 40Survey of the Natural Sciences

Which of the following best explains why the resting membrane potential of a typical neuron is close to the equilibrium potential for potassium?

  1. The sodium-potassium pump exports three K⁺ ions for every two Na⁺ ions imported.
  2. The concentration of K⁺ is higher outside the cell than inside.
  3. The membrane is highly permeable to K⁺ at rest due to open leak channels. Correct answer.
  4. Voltage-gated Na⁺ channels are open at rest.

Explanation

At rest, the neuronal membrane has many open K⁺ leak channels, making it far more permeable to K⁺ than to other ions. Therefore, the resting potential is driven largely by the K⁺ concentration gradient and approaches the K⁺ equilibrium potential.

Question 41Survey of the Natural Sciences

A gas initially at 300 K and 1 atm is compressed adiabatically to half its volume. Which of the following statements about the final state is correct?

  1. The temperature remains constant and the pressure doubles.
  2. The temperature decreases and the pressure decreases.
  3. The temperature increases and the pressure exactly doubles.
  4. The temperature increases and the pressure more than doubles. Correct answer.

Explanation

In an adiabatic compression, work is done on the gas, increasing its internal energy and thus its temperature. For an ideal gas, adiabatic compression follows PV^γ = constant, so if volume halves, pressure increases by a factor of 2^γ, which is more than 2.

Question 42Survey of the Natural Sciences

Which of the following is the major product of the reaction of 2-methyl-2-butene with HBr?

  1. 1-bromo-2-methylbutane
  2. 2-bromo-2-methylbutane Correct answer.
  3. 2-bromo-3-methylbutane
  4. 3-bromo-2-methylbutane

Explanation

Electrophilic addition of HBr to an alkene follows Markovnikov's rule, with the proton adding to the less substituted carbon to form the more stable carbocation. The tertiary carbocation at C2 leads to 2-bromo-2-methylbutane as the major product.

Question 43Survey of the Natural Sciences

Which of the following best explains the difference between the lock-and-key and induced-fit models of enzyme-substrate binding?

  1. Lock-and-key requires coenzymes, while induced-fit does not.
  2. Lock-and-key involves covalent bonding, while induced-fit involves only weak interactions.
  3. Induced fit allows the active site to change shape upon substrate binding, while lock-and-key assumes a rigid active site. Correct answer.
  4. Induced fit applies only to allosteric enzymes, while lock-and-key applies to all enzymes.

Explanation

The lock-and-key model proposes that the enzyme's active site is preformed and rigid, whereas the induced-fit model proposes that the active site adjusts its shape to fit the substrate more closely. This flexibility can increase catalytic efficiency and specificity.

Question 44Survey of the Natural Sciences

A population of birds has a range of beak sizes. During a drought, only birds with large beaks can crack the available hard seeds. Over several generations, the average beak size increases. This is an example of:

  1. Directional selection Correct answer.
  2. Stabilizing selection
  3. Disruptive selection
  4. Genetic drift

Explanation

Directional selection favors individuals at one extreme of the phenotypic range, shifting the population mean toward that extreme. Here, large beak size is favored, so the average increases over time.

Question 45Survey of the Natural Sciences

Which of the following statements about the light-dependent reactions of photosynthesis is correct?

  1. They consume ATP and NADPH to fix carbon.
  2. They occur in the stroma of the chloroplast.
  3. They generate ATP and NADPH, which are used in the Calvin cycle. Correct answer.
  4. They produce glucose directly from CO2 and H2O.

Explanation

The light-dependent reactions occur in the thylakoid membranes and convert light energy into chemical energy in the form of ATP and NADPH. These products are then used in the light-independent Calvin cycle to fix CO2 into sugars.

Question 46Survey of the Natural Sciences

A 0.10 M solution of a weak monoprotic acid has a pH of 3.0. What is the Ka of the acid?

  1. 1.0 × 10⁻⁶
  2. 1.0 × 10⁻³
  3. 1.0 × 10⁻⁵ Correct answer.
  4. 1.0 × 10⁻⁴

Explanation

From pH = 3.0, [H⁺] = 1.0 × 10⁻³ M. For a weak acid, Ka ≈ [H⁺]² / [HA] = (1.0 × 10⁻³)² / 0.10 = 1.0 × 10⁻⁵. The approximation is valid because [H⁺] is much smaller than the initial acid concentration.

Question 47Survey of the Natural Sciences

A 2 kg block moving at 4 m/s collides elastically with a stationary 3 kg block on a frictionless surface. What are the velocities of the 2 kg and 3 kg blocks immediately after the collision?

  1. 0.8 m/s and 3.2 m/s
  2. 0 m/s and 2.67 m/s
  3. −0.8 m/s and 3.2 m/s Correct answer.
  4. −1.6 m/s and 2.4 m/s

Explanation

For an elastic collision with a stationary target, v1' = (m1 − m2)/(m1 + m2) × v1 = (2−3)/5 × 4 = −0.8 m/s, and v2' = (2m1)/(m1 + m2) × v1 = (4/5) × 4 = 3.2 m/s. Both momentum and kinetic energy are conserved.

Question 48Survey of the Natural Sciences

Which of the following is the rate law for an SN1 reaction of a tertiary alkyl halide?

  1. Rate = k[nucleophile]
  2. Rate = k[alkyl halide] Correct answer.
  3. Rate = k[alkyl halide]²
  4. Rate = k[alkyl halide][nucleophile]

Explanation

SN1 reactions proceed via a two-step mechanism in which the rate-determining step is the unimolecular dissociation of the alkyl halide to form a carbocation. Therefore, the rate depends only on the concentration of the alkyl halide, giving first-order kinetics.

Question 49Survey of the Natural Sciences

A woman with blood type AB has a child with a man with blood type O. What are the possible blood types of their children?

  1. Type A, type B, or type AB
  2. Type AB only
  3. Type O only
  4. Type A or type B Correct answer.

Explanation

The woman with type AB has genotype IAIB, and the man with type O has genotype ii. Their children can inherit either IA or IB from the mother and i from the father, resulting in genotype IAi (type A) or IBi (type B). Thus, only types A and B are possible.

Question 50Survey of the Natural Sciences

A reaction has ΔH = +50 kJ/mol and ΔS = +100 J/(mol·K). At what temperature does the reaction become spontaneous under standard conditions?

  1. At all temperatures
  2. Above 500 K Correct answer.
  3. Above 0 K
  4. Below 500 K

Explanation

ΔG = ΔH − TΔS. For spontaneity, ΔG < 0, so T > ΔH/ΔS = 50,000 J/mol / 100 J/(mol·K) = 500 K. Since both ΔH and ΔS are positive, the reaction is entropy-driven and becomes spontaneous at high temperatures.