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WGU D425 INTRODUCTION TO CHEMISTRY
PA AND OA Actual Exam 2026/2027 Complete
Questions and Verified Answers with Detailed
Rationales Pass Guaranteed - A+ Graded
Q1: What is the mass number of an atom that contains 15 protons, 16 neutrons, and 15
electrons?
A. 15
B. 16
C. 31 [CORRECT]
D. 46
Correct Answer: C
Rationale: The mass number equals the sum of protons and neutrons (15 + 16 = 31); electrons
contribute negligible mass to atomic mass.
Q2: How many significant figures are in the measurement 0.004560 g?
A. 3
B. 4 [CORRECT]
C. 5
D. 7
Correct Answer: B
Rationale: Leading zeros are not significant; trailing zeros after the decimal are significant,
giving 4, 5, 6, and 0 as significant figures.
Q3: What is the molar mass of calcium carbonate (CaCO₃)?
A. 68.08 g/mol
B. 100.09 g/mol [CORRECT]
C. 128.10 g/mol
D. 156.12 g/mol
Correct Answer: B
Rationale: Molar mass = 40.08 (Ca) + 12.01 (C) + 3(16.00) (O) = 40.08 + 12.01 + 48.00 =
100.09 g/mol.
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Q4: How many moles of CO₂ are produced when 5.0 moles of propane (C₃H₈) undergo complete
combustion?
A. 5.0 mol
B. 10.0 mol
C. 15.0 mol [CORRECT]
D. 20.0 mol
Correct Answer: C
Rationale: The balanced equation C₃H₈ + 5O₂ → 3CO₂ + 4H₂O shows 3 moles CO₂ per 1 mole
C₃H₈; 5.0 mol × 3 = 15.0 mol CO₂.
Q5: What is the electron configuration for the chloride ion (Cl⁻)?
A. 1s² 2s² 2p⁶ 3s² 3p⁵
B. 1s² 2s² 2p⁶ 3s² 3p⁶ [CORRECT]
C. 1s² 2s² 2p⁶ 3s² 3p⁴
D. 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹
Correct Answer: B
Rationale: Chlorine gains one electron to form Cl⁻, achieving the stable argon configuration
with 18 electrons: 1s² 2s² 2p⁶ 3s² 3p⁶.
Q6: What type of bond forms between sodium and chlorine in NaCl?
A. Covalent bond
B. Polar covalent bond
C. Ionic bond [CORRECT]
D. Metallic bond
Correct Answer: C
Rationale: Sodium (metal) transfers an electron to chlorine (nonmetal), creating oppositely
charged ions held together by electrostatic attraction—characteristic of ionic bonding.
Q7: Calculate the density of a substance with mass 45.0 g and volume 15.0 mL.
A. 0.333 g/mL
B. 2.50 g/mL
C. 3.00 g/mL [CORRECT]
D. 675 g/mL
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Correct Answer: C
Rationale: Density = mass/volume = 45.0 g / 15.0 mL = 3.00 g/mL.
Q8: What is the oxidation number of sulfur in H₂SO₄?
A. +4
B. +6 [CORRECT]
C. +2
D. -2
Correct Answer: B
Rationale: Hydrogen is +1 (2 × +1 = +2), oxygen is -2 (4 × -2 = -8); sulfur must be +6 to
balance: +2 + x + (-8) = 0, therefore x = +6.
Q9: How many total atoms are in 2.5 moles of water (H₂O)?
A. 7.5 × 10²³ atoms
B. 1.5 × 10²⁴ atoms
C. 4.5 × 10²⁴ atoms [CORRECT]
D. 2.5 × 10²⁴ atoms
Correct Answer: C
Rationale: Each H₂O molecule contains 3 atoms; 2.5 mol × 6.022 × 10²³ molecules/mol × 3
atoms/molecule = 4.5 × 10²⁴ atoms.
Q10: What is the pH of a solution with [H⁺] = 1.0 × 10⁻⁹ M?
A. 5
B. 7
C. 9 [CORRECT]
D. -9
Correct Answer: C
Rationale: pH = -log[H⁺] = -log(1.0 × 10⁻⁹) = 9, indicating a basic solution.
Q11: Which element has the highest electronegativity?
A. Sodium
B. Fluorine [CORRECT]
C. Cesium
D. Calcium
WGU D425 INTRODUCTION TO CHEMISTRY
PA AND OA Actual Exam 2026/2027 Complete
Questions and Verified Answers with Detailed
Rationales Pass Guaranteed - A+ Graded
Q1: What is the mass number of an atom that contains 15 protons, 16 neutrons, and 15
electrons?
A. 15
B. 16
C. 31 [CORRECT]
D. 46
Correct Answer: C
Rationale: The mass number equals the sum of protons and neutrons (15 + 16 = 31); electrons
contribute negligible mass to atomic mass.
Q2: How many significant figures are in the measurement 0.004560 g?
A. 3
B. 4 [CORRECT]
C. 5
D. 7
Correct Answer: B
Rationale: Leading zeros are not significant; trailing zeros after the decimal are significant,
giving 4, 5, 6, and 0 as significant figures.
Q3: What is the molar mass of calcium carbonate (CaCO₃)?
A. 68.08 g/mol
B. 100.09 g/mol [CORRECT]
C. 128.10 g/mol
D. 156.12 g/mol
Correct Answer: B
Rationale: Molar mass = 40.08 (Ca) + 12.01 (C) + 3(16.00) (O) = 40.08 + 12.01 + 48.00 =
100.09 g/mol.
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Q4: How many moles of CO₂ are produced when 5.0 moles of propane (C₃H₈) undergo complete
combustion?
A. 5.0 mol
B. 10.0 mol
C. 15.0 mol [CORRECT]
D. 20.0 mol
Correct Answer: C
Rationale: The balanced equation C₃H₈ + 5O₂ → 3CO₂ + 4H₂O shows 3 moles CO₂ per 1 mole
C₃H₈; 5.0 mol × 3 = 15.0 mol CO₂.
Q5: What is the electron configuration for the chloride ion (Cl⁻)?
A. 1s² 2s² 2p⁶ 3s² 3p⁵
B. 1s² 2s² 2p⁶ 3s² 3p⁶ [CORRECT]
C. 1s² 2s² 2p⁶ 3s² 3p⁴
D. 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹
Correct Answer: B
Rationale: Chlorine gains one electron to form Cl⁻, achieving the stable argon configuration
with 18 electrons: 1s² 2s² 2p⁶ 3s² 3p⁶.
Q6: What type of bond forms between sodium and chlorine in NaCl?
A. Covalent bond
B. Polar covalent bond
C. Ionic bond [CORRECT]
D. Metallic bond
Correct Answer: C
Rationale: Sodium (metal) transfers an electron to chlorine (nonmetal), creating oppositely
charged ions held together by electrostatic attraction—characteristic of ionic bonding.
Q7: Calculate the density of a substance with mass 45.0 g and volume 15.0 mL.
A. 0.333 g/mL
B. 2.50 g/mL
C. 3.00 g/mL [CORRECT]
D. 675 g/mL
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Correct Answer: C
Rationale: Density = mass/volume = 45.0 g / 15.0 mL = 3.00 g/mL.
Q8: What is the oxidation number of sulfur in H₂SO₄?
A. +4
B. +6 [CORRECT]
C. +2
D. -2
Correct Answer: B
Rationale: Hydrogen is +1 (2 × +1 = +2), oxygen is -2 (4 × -2 = -8); sulfur must be +6 to
balance: +2 + x + (-8) = 0, therefore x = +6.
Q9: How many total atoms are in 2.5 moles of water (H₂O)?
A. 7.5 × 10²³ atoms
B. 1.5 × 10²⁴ atoms
C. 4.5 × 10²⁴ atoms [CORRECT]
D. 2.5 × 10²⁴ atoms
Correct Answer: C
Rationale: Each H₂O molecule contains 3 atoms; 2.5 mol × 6.022 × 10²³ molecules/mol × 3
atoms/molecule = 4.5 × 10²⁴ atoms.
Q10: What is the pH of a solution with [H⁺] = 1.0 × 10⁻⁹ M?
A. 5
B. 7
C. 9 [CORRECT]
D. -9
Correct Answer: C
Rationale: pH = -log[H⁺] = -log(1.0 × 10⁻⁹) = 9, indicating a basic solution.
Q11: Which element has the highest electronegativity?
A. Sodium
B. Fluorine [CORRECT]
C. Cesium
D. Calcium
