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ORELA Chemistry (NT321) study materials
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ORELA Chemistry (NT321) practice questions

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Question 1Subarea I

Which statement correctly describes the arrangement of particles in a solid ionic compound such as sodium chloride at room temperature?

  1. Cations and anions move freely past one another throughout the entire solid.
  2. Electrons are shared between adjacent sodium and chloride atoms to form covalent bonds.
  3. Ions are held in a fixed three-dimensional lattice by electrostatic attraction between oppositely charged ions. Correct answer.
  4. Neutral molecules are packed together and held by London dispersion forces only.

Explanation

An ionic solid consists of a repeating lattice of cations and anions. Each ion is surrounded by ions of opposite charge, and strong electrostatic attraction holds the lattice in fixed positions, which is why ionic solids are hard and have high melting points.

Question 2Subarea I

A neutral atom of an element has the electron configuration 1s2 2s2 2p6 3s2 3p4. In which group of the periodic table does this element belong?

  1. Group 18
  2. Group 12
  3. Group 16 Correct answer.
  4. Group 14

Explanation

The configuration ends in 3s2 3p4, giving six valence electrons in the third shell. Elements with six valence electrons occupy Group 16, which includes oxygen and sulfur.

Question 3Subarea I

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

  1. Metallic character
  2. First ionization energy Correct answer.
  3. Number of neutron-rich isotopes
  4. Atomic radius

Explanation

Across a period, effective nuclear charge rises while electrons enter the same shell, so the outermost electron is held more tightly. This raises first ionization energy and generally decreases atomic radius and metallic character.

Question 4Subarea I

How many significant figures are in the measured value 0.004070 g?

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

Explanation

Leading zeros before the first nonzero digit are placeholders and are not significant. The digits 4, 0, 7, and the trailing zero after the decimal are significant, giving four significant figures.

Question 5Subarea I

A sample of gas occupies 2.00 L at 300 K and constant pressure. What volume does it occupy at 450 K?

  1. 3.00 L Correct answer.
  2. 1.33 L
  3. 4.50 L
  4. 2.67 L

Explanation

At constant pressure, Charles's law gives V1/T1 = V2/T2, so V2 = 2.00 L × (450 K / 300 K) = 3.00 L. Temperature must be expressed in kelvin for the ratio to hold.

Question 6Subarea I

Which pair of species constitutes a conjugate acid–base pair?

  1. CO2 and CO
  2. H2O and NaCl
  3. NH3 and NH4+ Correct answer.
  4. HCl and NaOH

Explanation

A conjugate acid–base pair differs by exactly one proton. NH4+ is formed when NH3 accepts a proton, so the two are a conjugate pair.

Question 7Subarea I

Which type of reaction is represented by the equation AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq)?

  1. Combustion
  2. Precipitation Correct answer.
  3. Acid–base neutralization
  4. Single replacement

Explanation

Two soluble salts exchange ions, and AgCl forms as an insoluble solid that separates from solution. Formation of an insoluble product from solution is the defining feature of a precipitation reaction.

Question 8Subarea I

Two ions each contain ten electrons. One has eleven protons and the other twelve. Why must they be ions of different elements?

  1. Their electron numbers are identical
  2. Their electrical charges must be identical
  3. They must have equal numbers of neutrons
  4. Their proton numbers differ Correct answer.

Explanation

Proton number defines element identity. Eleven protons identify sodium and twelve identify magnesium, even though both ions have ten electrons and are therefore isoelectronic rather than the same element.

Question 9Subarea I

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

  1. CH2O Correct answer.
  2. C2H6O
  3. C2H4O
  4. CHO

Explanation

Dividing each percentage by atomic mass gives 3.33 mol C, 6.7 mol H, and 3.33 mol O per 100 g. Dividing by the smallest value yields a 1:2:1 ratio, so the empirical formula is CH2O.

Question 10Subarea I

What is the oxidation state of manganese in the permanganate ion, MnO4−?

  1. +2
  2. +7 Correct answer.
  3. +8
  4. +4

Explanation

Each oxygen is assigned −2, so the four oxygens total −8. Because the ion carries an overall charge of −1, manganese must be +7 to satisfy −8 + 7 = −1.

Question 11Subarea I

Which change shifts the equilibrium of the endothermic reaction N2O4(g) ⇌ 2NO2(g) toward the products?

  1. Raising the temperature at constant pressure Correct answer.
  2. Adding a catalyst at constant temperature
  3. Removing some NO2 from the mixture
  4. Increasing the pressure at constant temperature

Explanation

For an endothermic forward reaction, raising the temperature adds heat to the reactant side, and Le Châtelier's principle drives the system toward products. Removing NO2 would also shift right, but among the listed choices only the temperature increase favors products without removing material.

Question 12Subarea I

A solution has a hydroxide ion concentration of 1.0 × 10−4 M at 25 °C. What is its pH?

  1. 14.0
  2. 10.0 Correct answer.
  3. 7.0
  4. 4.0

Explanation

At 25 °C the ion product of water gives [H+] = 1.0 × 10−14 / 1.0 × 10−4 = 1.0 × 10−10 M. The pH is the negative logarithm of that value, which equals 10.0, consistent with a basic solution.

Question 13Subarea I

In the reaction Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s), which species is oxidized?

  1. Zn(s) Correct answer.
  2. Cu2+(aq)
  3. Zn2+(aq)
  4. Cu(s)

Explanation

Zinc loses two electrons, increasing its oxidation state from 0 to +2, which is oxidation. The copper ion gains those electrons and is reduced from +2 to 0.

Question 14Subarea I

Methanol has a much higher boiling point than methane. Which structural feature enables the additional strong intermolecular attraction in methanol?

  1. Complete transfer of an electron from carbon to every hydrogen
  2. An oxygen-hydrogen bond that permits hydrogen bonding between molecules Correct answer.
  3. A lattice made entirely of metal cations
  4. A larger number of carbon atoms than methane

Explanation

Methanol contains an O-H group that can form hydrogen bonds between molecules. Methane lacks this group and does not exhibit comparable self hydrogen bonding, contributing to its much lower boiling point.

Question 15Subarea I

A reaction has an activation energy of 50 kJ/mol without a catalyst and 30 kJ/mol with a catalyst. What effect does the catalyst have on the reaction?

  1. It lowers the activation energy and increases the rate of both forward and reverse reactions. Correct answer.
  2. It increases the activation energy of the reverse reaction only.
  3. It increases the enthalpy change of the reaction.
  4. It shifts the equilibrium position toward the products.

Explanation

A catalyst provides an alternative pathway with a lower activation energy, so more collisions have sufficient energy and the rate increases. Because it lowers the barrier for both directions equally, it does not change the equilibrium constant or the enthalpy change.

Question 16Subarea I

Which electron configuration represents the ground state of a neutral chromium atom (Z = 24)?

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

Explanation

Chromium is an exception to the usual filling order because a half-filled 3d subshell with one 4s electron gives extra exchange stability. The accepted ground-state configuration is [Ar] 4s1 3d5.

Question 17Subarea I

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

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

Explanation

The angular momentum quantum number l can range from 0 to n − 1, and ml ranges from −l to +l. For n = 2, l = 1, and ml = −1, all conditions are satisfied, and ms = −1/2 is a valid spin value.

Question 18Subarea I

A 25.0 mL sample of 0.100 M HCl is titrated with 0.100 M NaOH. What volume of NaOH is required to reach the equivalence point?

  1. 50.0 mL
  2. 12.5 mL
  3. 2.50 mL
  4. 25.0 mL Correct answer.

Explanation

HCl and NaOH react in a 1:1 mole ratio. Because the concentrations are equal, the equivalence point requires equal volumes, so 25.0 mL of NaOH neutralizes 25.0 mL of HCl.

Question 19Subarea I

Two samples of an ideal gas at the same temperature have equal numbers of molecules. Which statement about the samples must be true?

  1. They have the same mass and the same density.
  2. They have the same average kinetic energy and occupy the same volume at the same pressure. Correct answer.
  3. They have the same molar mass and the same effusion rate.
  4. They have the same molecular diameter and the same van der Waals constants.

Explanation

Average kinetic energy of gas molecules depends only on absolute temperature, so equal temperatures mean equal average kinetic energy. Avogadro's law then gives equal volumes for equal molecule counts at the same pressure.

Question 20Subarea I

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

  1. The second electron experiences greater shielding because a new shell is added.
  2. The second electron is removed from a higher principal energy level than the first.
  3. The second electron is removed from a positive ion and feels a stronger net attraction to the nucleus. Correct answer.
  4. The nucleus gains an extra proton after the first electron is removed.

Explanation

After one electron is removed, the remaining electrons are pulled in more strongly by the same nuclear charge, and the ion already carries a positive charge. Removing the next electron therefore requires substantially more energy.

Question 21Subarea I

A galvanic cell is constructed with a standard zinc electrode (E° = −0.76 V) and a standard copper electrode (E° = +0.34 V). What is the standard cell potential?

  1. −0.42 V
  2. +1.10 V Correct answer.
  3. −1.10 V
  4. +0.42 V

Explanation

In a galvanic cell the more positive electrode is the cathode, so copper is reduced and zinc is oxidized. The cell potential is E°cathode − E°anode = 0.34 V − (−0.76 V) = +1.10 V.

Question 22Subarea I

For the reaction 2A + B → products, doubling [A] while holding [B] constant quadruples the rate, and doubling [B] while holding [A] constant doubles the rate. What is the rate law?

  1. Rate = k[A][B]2
  2. Rate = k[A]2[B]2
  3. Rate = k[A][B]
  4. Rate = k[A]2[B] Correct answer.

Explanation

The rate depends on the square of [A] because doubling [A] quadruples the rate, and on the first power of [B] because doubling [B] doubles the rate. Combining these orders gives Rate = k[A]2[B].

Question 23Subarea I

A buffer is prepared from equal concentrations of acetic acid and sodium acetate. Which statement correctly describes its behavior when a small amount of strong acid is added?

  1. Acetic acid molecules consume added protons, and the pH rises sharply.
  2. Added protons react with water to increase the hydroxide concentration, and the pH falls sharply.
  3. Added protons are neutralized by sodium ions, and the pH stays exactly constant.
  4. Acetate ions consume added protons, and the pH changes only slightly. Correct answer.

Explanation

In an acetic acid–acetate buffer, the conjugate base acetate neutralizes added strong acid by accepting protons to form more acetic acid. Because the ratio of acid to conjugate base changes only slightly, the pH decreases only a little.

Question 24Subarea I

Which description correctly accounts for the shape of a molecule of sulfur dioxide, SO2?

  1. Linear, because two electron domains around sulfur adopt a 180° arrangement.
  2. Tetrahedral, because sulfur is bonded to two oxygen atoms and two lone pairs.
  3. Bent, because sulfur has three electron domains with one lone pair, giving a bond angle near 120°. Correct answer.
  4. Trigonal planar, because all three electron domains around sulfur are bonding pairs.

Explanation

Sulfur in SO2 has three electron domains: two bonding pairs and one lone pair. The electron-domain geometry is trigonal planar, but the lone pair compresses the O–S–O angle, producing a bent molecular shape.

Question 25Subarea I

A first-order reaction has a half-life of 20 minutes. Starting with 0.80 M reactant, what concentration remains after 60 minutes?

  1. 0.10 M Correct answer.
  2. 0.05 M
  3. 0.20 M
  4. 0.40 M

Explanation

Sixty minutes corresponds to three half-lives of 20 minutes each. The concentration is halved three times: 0.80 M → 0.40 M → 0.20 M → 0.10 M.

Question 26Subarea I

Which statement correctly describes the number of significant figures in the measured value 0.004560 g?

  1. Three significant figures, because the trailing zero is not counted
  2. Six significant figures, because every digit shown is counted
  3. Two significant figures, because only the nonzero digits count
  4. Four significant figures, because the leading zeros are not counted Correct answer.

Explanation

Leading zeros that merely position the decimal point are never significant, so the 4, 5, and final trailing 6 are counted, and the zero between 5 and 6 is also significant. The value 0.004560 therefore has four significant figures.

Question 27Subarea I

An atom of an isotope is described by the notation 37Cl with atomic number 17. How many neutrons does one atom of this isotope contain?

  1. 20 Correct answer.
  2. 37
  3. 54
  4. 17

Explanation

The mass number (37) equals protons plus neutrons, and the atomic number (17) gives the proton count. Subtracting 17 from 37 leaves 20 neutrons in the nucleus of this chlorine isotope.

Question 28Subarea I

Which name is correct for the compound with the formula Fe2O3?

  1. Iron oxide
  2. Iron(III) oxide Correct answer.
  3. Diiron trioxide
  4. Iron(II) oxide

Explanation

Oxygen takes the −2 oxidation state, so three oxide ions carry a total charge of −6, requiring the two iron ions to contribute +6, or +3 each. The Stock system names the metal with its charge in Roman numerals, giving iron(III) oxide.

Question 29Subarea I

Which particle is emitted when a nucleus of carbon-14 decays to form nitrogen-14?

  1. An alpha particle
  2. A neutron
  3. A beta particle Correct answer.
  4. A gamma ray

Explanation

In carbon-14 the atomic number rises from 6 to 7 when nitrogen-14 forms, while the mass number stays at 14. That change corresponds to conversion of a neutron into a proton with emission of a beta particle (an electron), which carries away the charge.

Question 30Subarea I

A sealed rigid container holds a gas at 300 K and 1.0 atm. If the gas is heated to 600 K while the volume is held constant, what is the new pressure?

  1. 2.0 atm Correct answer.
  2. 1.0 atm
  3. 0.50 atm
  4. 4.0 atm

Explanation

Gay-Lussac's law states that at constant volume, pressure is directly proportional to absolute temperature. Doubling the temperature from 300 K to 600 K therefore doubles the pressure from 1.0 atm to 2.0 atm.

Question 31Subarea I

What is the molarity of a solution prepared by dissolving 5.85 g of NaCl (molar mass 58.5 g/mol) in enough water to make 500. mL of solution?

  1. 1.00 M
  2. 0.200 M Correct answer.
  3. 0.100 M
  4. 0.500 M

Explanation

Dividing 5.85 g by 58.5 g/mol gives 0.100 mol of NaCl. Dividing that amount by 0.500 L of solution yields 0.200 M, since molarity is moles of solute per liter of solution.

Question 32Subarea I

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

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

Explanation

Across a period, protons are added to the nucleus while electrons enter the same principal shell, so the effective nuclear charge felt by the outer electrons rises. That stronger attraction pulls the electron cloud closer, shrinking the atomic radius.

Question 33Subarea I

Which statement best explains why a sample of solid sodium chloride conducts electricity only after it is melted or dissolved?

  1. Melting converts the ionic solid into neutral molecules that carry charge
  2. Covalent bonds in the solid are broken to release free electrons when it melts
  3. Ions in the solid lattice are locked in place and become mobile when the lattice is broken Correct answer.
  4. Dissolving removes electrons from the ions, allowing current to flow

Explanation

An ionic solid consists of a lattice of fixed ions that cannot migrate, so it does not conduct. Melting or dissolving frees those ions to move, allowing them to carry charge through the material.

Question 34Subarea I

A sample of an ideal gas occupies 2.0 L at 1.5 atm. What volume will it occupy at 3.0 atm if the temperature is held constant?

  1. 0.50 L
  2. 4.0 L
  3. 3.0 L
  4. 1.0 L Correct answer.

Explanation

Boyle's law states that at constant temperature, pressure and volume are inversely proportional, so P1V1 equals P2V2. Here 1.5 atm times 2.0 L equals 3.0, and dividing by 3.0 atm gives 1.0 L.

Question 35Subarea I

Which statement correctly compares the first ionization energy of potassium with that of sodium?

  1. Sodium has the higher value because its valence electron is closer to the nucleus Correct answer.
  2. Potassium has the higher value because its valence electron is in a higher-energy orbital
  3. Potassium has the higher value because it has more protons
  4. The two values are equal because both are alkali metals

Explanation

The valence electron of sodium lies in the n = 3 shell, closer to the nucleus and less shielded than the n = 4 electron of potassium. The weaker attraction in potassium makes its electron easier to remove, so sodium has the higher first ionization energy.

Question 36Subarea I

A 2.00 g sample of an unknown hydrocarbon is burned completely, producing 6.29 g of CO2 and 2.57 g of H2O. What is the empirical formula of the compound?

  1. CH2 Correct answer.
  2. C3H8
  3. C2H5
  4. C4H9

Explanation

The CO2 contains 6.29 g × (12.01/44.01) ≈ 1.72 g of carbon, which is 0.143 mol, and the water contains 2.57 g × (2.016/18.02) ≈ 0.288 g of hydrogen, which is 0.286 mol. The mole ratio of H to C is about 2:1, giving the empirical formula CH2.

Question 37Subarea I

Which statement correctly explains why a solution of ammonium chloride in water is acidic?

  1. The chloride ion reacts with water to release hydroxide ions
  2. Ammonium chloride dissolves without reacting, leaving the pH unchanged
  3. The ammonium ion donates a proton to water, increasing the hydronium ion concentration Correct answer.
  4. The ammonium ion accepts a proton from water, forming ammonia and hydronium ions

Explanation

The ammonium ion is the conjugate acid of the weak base ammonia, so it acts as a Brønsted acid and transfers a proton to water. This raises the hydronium ion concentration and makes the solution acidic, while the chloride ion is a negligible base.

Question 38Subarea I

Which set of coefficients balances the equation __C3H8 + __O2 → __CO2 + __H2O using the smallest whole numbers?

  1. 1, 4, 3, 4
  2. 1, 5, 3, 4 Correct answer.
  3. 2, 10, 6, 8
  4. 1, 3, 3, 4

Explanation

Balancing carbon gives 3 CO2 and balancing hydrogen gives 4 H2O, which together require 6 + 4 = 10 oxygen atoms, or 5 O2 molecules. The coefficients 1, 5, 3, 4 are the smallest whole numbers that conserve every element.

Question 39Subarea I

Which statement correctly describes the entropy change when a gas is compressed isothermally from 4.0 L to 1.0 L?

  1. Entropy stays the same because the temperature is constant
  2. Entropy decreases because the molecules occupy a smaller volume with fewer accessible microstates Correct answer.
  3. Entropy increases because the gas is doing work on the surroundings
  4. Entropy decreases because the gas absorbs heat from the surroundings

Explanation

Entropy depends on the number of accessible microstates, and confining the same number of molecules to a smaller volume reduces that number. The change is ΔS = nR ln(V2/V1), which is negative here, so entropy decreases even though temperature is unchanged.

Question 40Subarea I

A galvanic cell is built from a standard silver electrode (E° = +0.80 V) and a standard nickel electrode (E° = −0.25 V). What is the standard cell potential?

  1. +0.30 V
  2. +0.55 V
  3. −1.05 V
  4. +1.05 V Correct answer.

Explanation

The standard cell potential equals the reduction potential of the cathode minus that of the anode. Silver, with the more positive value, is reduced at the cathode, so E°cell = 0.80 V − (−0.25 V) = 1.05 V, a positive value consistent with a spontaneous reaction.

Question 41Subarea II

A neutral atom of an element has the ground-state electron configuration 1s² 2s² 2p⁶ 3s² 3p⁴. Which element is this?

  1. Sulfur Correct answer.
  2. Oxygen
  3. Selenium
  4. Phosphorus

Explanation

The configuration totals 2+2+6+2+4 = 16 electrons, and a neutral atom has equal numbers of protons and electrons, so the atomic number is 16. Atomic number 16 corresponds to sulfur. The outer-shell pattern 3s² 3p⁴ also places it in group 16, period 3.

Question 42Subarea II

Which statement correctly describes the trend in first ionization energy across period 3 from sodium to argon?

  1. It decreases steadily because atomic radius grows.
  2. It remains constant because the number of shells is fixed.
  3. It increases overall, with local dips at aluminum and sulfur. Correct answer.
  4. It increases steadily with no exceptions.

Explanation

Across a period the nuclear charge rises while electrons enter the same shell, so ionization energy generally increases. Small dips occur at aluminum, where the electron removed comes from a 3p orbital rather than a filled 3s, and at sulfur, where removing one 3p electron relieves electron–electron repulsion in a paired orbital.

Question 43Subarea II

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

  1. CHO
  2. C₂H₄O
  3. CH₂O Correct answer.
  4. C₂H₆O

Explanation

Assume 100 g, giving 40.0 g C, 6.7 g H, and 53.3 g O. Dividing by the atomic masses gives 3.33 mol C, 6.7 mol H, and 3.33 mol O, and dividing each by the smallest value gives a 1:2:1 ratio. The empirical formula is therefore CH₂O.

Question 44Subarea II

For the reaction N₂(g) + 3H₂(g) ⇌ 2NH₃(g), which change shifts the equilibrium toward the products?

  1. Raising the temperature
  2. Adding a catalyst
  3. Increasing the volume of the container
  4. Removing ammonia as it forms Correct answer.

Explanation

Removing a product lowers its concentration, so the system responds by shifting toward the products to partially restore it. The reaction produces fewer gas moles than it consumes, so increasing volume favors the reactants, and a catalyst changes only the rate, not the position of equilibrium.

Question 45Subarea II

Which of the following is the conjugate base of the dihydrogen phosphate ion, H₂PO₄⁻?

  1. H₂PO₃⁻
  2. PO₄³⁻
  3. HPO₄²⁻ Correct answer.
  4. H₃PO₄

Explanation

A conjugate base is formed by removing one proton from the acid. Removing H⁺ from H₂PO₄⁻ leaves HPO₄²⁻, with the charge decreasing by one unit as the proton leaves.

Question 46Subarea II

In a galvanic cell, oxidation occurs at the anode. Which description of the anode is correct?

  1. It is the positive electrode and releases electrons to the cathode.
  2. It is the negative electrode and is where reduction takes place.
  3. It is the positive electrode and gains mass as metal deposits.
  4. It is the negative electrode and loses mass as metal dissolves. Correct answer.

Explanation

In a galvanic cell the anode is where oxidation occurs, releasing electrons that travel through the external circuit to the cathode. Because metal atoms leave the electrode as ions, the anode loses mass, and it serves as the negative terminal of the cell.

Question 47Subarea II

The half-life of a particular first-order reaction is 30 minutes. What fraction of the original reactant remains after 90 minutes?

  1. One-sixteenth
  2. One-quarter
  3. One-half
  4. One-eighth Correct answer.

Explanation

Ninety minutes corresponds to three half-lives (3 × 30 min). Each half-life halves the remaining amount, so the fraction is (1/2)³ = 1/8 of the original quantity.

Question 48Subarea II

Which quantum number determines the shape of an atomic orbital?

  1. Spin quantum number ms
  2. Principal quantum number n
  3. Angular momentum quantum number ℓ Correct answer.
  4. Magnetic quantum number mℓ

Explanation

The angular momentum quantum number ℓ defines the subshell and therefore the orbital shape, with ℓ = 0, 1, 2 corresponding to s, p, and d orbitals. The principal quantum number sets size and energy level, while mℓ and ms describe orientation and spin.

Question 49Subarea II

A gas occupies 2.0 L at 300 K and 1.0 atm. If the temperature is raised to 600 K at constant pressure, what volume does the gas occupy?

  1. 8.0 L
  2. 1.0 L
  3. 4.0 L Correct answer.
  4. 2.0 L

Explanation

Charles's law states that volume is directly proportional to absolute temperature at constant pressure, so V₂ = V₁(T₂/T₁). Substituting gives 2.0 L × (600 K / 300 K) = 4.0 L.

Question 50Subarea II

Which of the following sets of quantum numbers is not permitted for an electron in an atom?

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

Explanation

The angular momentum quantum number must satisfy ℓ ≤ n − 1, so for n = 2 the only allowed values are ℓ = 0 and ℓ = 1. The set with n = 2 and ℓ = 2 violates this rule and cannot describe an electron.