WGU D425 INTRODUCTION TO CHEMISTRY -PA AND OA EXAM – QUESTIONS
AND ANSWERS | VERIFIED AND WELL DETAILED ANSWERS | PLUS RATIONALES
| DOWNLOAD AND PASS | LATEST EXAM UPDATE 2026/2027
Core Domains
1. Atomic Structure and Periodic Trends
2. Chemical Bonding and Molecular Geometry
3. Stoichiometry and Chemical Reactions
4. Thermochemistry and Thermodynamics
5. Kinetics and Chemical Equilibrium
6. Acids, Bases, and Aqueous Equilibria
7. Electrochemistry and Redox Reactions
8. Organic Chemistry and Biochemistry Fundamentals
9. Nuclear Chemistry
Introduction
This comprehensive assessment is designed to evaluate your mastery of
foundational and applied chemistry concepts as required for the WGU D425
examination. It covers a broad spectrum of topics, from atomic theory to complex
biochemical reactions, emphasizing the quantitative and qualitative skills necessary
for professional application. The examination utilizes a multiple-choice and
scenario-based format to test your knowledge, critical thinking, and decision-
making abilities. Each question is crafted to not only assess recall but also your
capacity to integrate concepts and solve real-world chemical problems, ensuring
you are well-prepared for both the PA and OA.
Section One: Questions 1–50
1. Which of the following statements best describes the law of conservation of
mass?
,A. Matter can be created in a nuclear reaction.
B. Mass is neither created nor destroyed in a chemical reaction.
C. The mass of the products is always greater than the mass of the reactants.
D. Mass can be converted to energy but not destroyed.
🟢 Correct Answer: B. Mass is neither created nor destroyed in a chemical
reaction.
🔴 Explanation: The law of conservation of mass states that in a closed system,
matter is neither created nor destroyed. Therefore, the total mass of the reactants
must equal the total mass of the products in a chemical reaction.
2. A sample of an unknown gas effuses 1.5 times faster than oxygen gas (O2).
What is the approximate molar mass of the unknown gas?
A. 18 g/mol
B. 28 g/mol
C. 32 g/mol
D. 72 g/mol
🟢 Correct Answer: B. 28 g/mol
🔴 Explanation: Graham's law of effusion states (Rate1/Rate2) = sqrt(M2/M1). If
the unknown gas effuses 1.5 times faster, then 1.5 = sqrt(32/M_unknown).
Squaring gives 2.25 = 32/M_unknown, so M_unknown = 32/2.25 = 14.2 g/mol.
The closest value is 28 g/mol, which is N2.
3. Which of the following quantum numbers defines the shape of an orbital?
A. Principal quantum number (n)
B. Azimuthal quantum number (l)
,C. Magnetic quantum number (ml)
D. Spin quantum number (ms)
🟢 Correct Answer: B. Azimuthal quantum number (l)
🔴 Explanation: The azimuthal quantum number (l) determines the shape of an
orbital (s, p, d, f). The principal quantum number (n) defines the energy level, the
magnetic quantum number (ml) defines the spatial orientation, and the spin
quantum number (ms) defines the spin of the electron.
4. A reaction has a ΔH of -100 kJ and a ΔS of +50 J/K. At what temperature (in
Kelvin) will this reaction become non-spontaneous?
A. 2000 K
B. 500 K
C. 200 K
D. This reaction is spontaneous at all temperatures.
🟢 Correct Answer: D. This reaction is spontaneous at all temperatures.
🔴 Explanation: A reaction with a negative ΔH and a positive ΔS will have a
negative ΔG (ΔG = ΔH - TΔS) at all temperatures. Therefore, it is spontaneous at
all temperatures.
5. What is the maximum number of electrons that can be accommodated in the
third principal energy level (n=3)?
A. 8
B. 18
C. 32
D. 2
, 🟢 Correct Answer: B. 18
🔴 Explanation: The maximum number of electrons in a shell is given by 2n². For
n=3, 2 * 3² = 18 electrons.
6. A solution has a pH of 10. What is the concentration of hydroxide ions [OH-]
in the solution?
A. 1 x 10⁻¹⁰ M
B. 1 x 10⁻⁴ M
C. 1 x 10⁴ M
D. 1 x 10⁻¹⁴ M
🟢 Correct Answer: B. 1 x 10⁻⁴ M
🔴 Explanation: pH + pOH = 14. If pH is 10, pOH is 4. [OH-] = 10^-pOH = 1 x
10⁻⁴ M.
7. A 1.0 M solution of which of the following salts would have the highest pH?
A. NaCl
B. NH4Cl
C. Na2CO3
D. KNO3
🟢 Correct Answer: C. Na2CO3
🔴 Explanation: Na2CO3 is a salt of a strong base (NaOH) and a weak acid
(H2CO3). Its aqueous solution is basic due to the hydrolysis of the carbonate ion,
resulting in the highest pH among the options.
AND ANSWERS | VERIFIED AND WELL DETAILED ANSWERS | PLUS RATIONALES
| DOWNLOAD AND PASS | LATEST EXAM UPDATE 2026/2027
Core Domains
1. Atomic Structure and Periodic Trends
2. Chemical Bonding and Molecular Geometry
3. Stoichiometry and Chemical Reactions
4. Thermochemistry and Thermodynamics
5. Kinetics and Chemical Equilibrium
6. Acids, Bases, and Aqueous Equilibria
7. Electrochemistry and Redox Reactions
8. Organic Chemistry and Biochemistry Fundamentals
9. Nuclear Chemistry
Introduction
This comprehensive assessment is designed to evaluate your mastery of
foundational and applied chemistry concepts as required for the WGU D425
examination. It covers a broad spectrum of topics, from atomic theory to complex
biochemical reactions, emphasizing the quantitative and qualitative skills necessary
for professional application. The examination utilizes a multiple-choice and
scenario-based format to test your knowledge, critical thinking, and decision-
making abilities. Each question is crafted to not only assess recall but also your
capacity to integrate concepts and solve real-world chemical problems, ensuring
you are well-prepared for both the PA and OA.
Section One: Questions 1–50
1. Which of the following statements best describes the law of conservation of
mass?
,A. Matter can be created in a nuclear reaction.
B. Mass is neither created nor destroyed in a chemical reaction.
C. The mass of the products is always greater than the mass of the reactants.
D. Mass can be converted to energy but not destroyed.
🟢 Correct Answer: B. Mass is neither created nor destroyed in a chemical
reaction.
🔴 Explanation: The law of conservation of mass states that in a closed system,
matter is neither created nor destroyed. Therefore, the total mass of the reactants
must equal the total mass of the products in a chemical reaction.
2. A sample of an unknown gas effuses 1.5 times faster than oxygen gas (O2).
What is the approximate molar mass of the unknown gas?
A. 18 g/mol
B. 28 g/mol
C. 32 g/mol
D. 72 g/mol
🟢 Correct Answer: B. 28 g/mol
🔴 Explanation: Graham's law of effusion states (Rate1/Rate2) = sqrt(M2/M1). If
the unknown gas effuses 1.5 times faster, then 1.5 = sqrt(32/M_unknown).
Squaring gives 2.25 = 32/M_unknown, so M_unknown = 32/2.25 = 14.2 g/mol.
The closest value is 28 g/mol, which is N2.
3. Which of the following quantum numbers defines the shape of an orbital?
A. Principal quantum number (n)
B. Azimuthal quantum number (l)
,C. Magnetic quantum number (ml)
D. Spin quantum number (ms)
🟢 Correct Answer: B. Azimuthal quantum number (l)
🔴 Explanation: The azimuthal quantum number (l) determines the shape of an
orbital (s, p, d, f). The principal quantum number (n) defines the energy level, the
magnetic quantum number (ml) defines the spatial orientation, and the spin
quantum number (ms) defines the spin of the electron.
4. A reaction has a ΔH of -100 kJ and a ΔS of +50 J/K. At what temperature (in
Kelvin) will this reaction become non-spontaneous?
A. 2000 K
B. 500 K
C. 200 K
D. This reaction is spontaneous at all temperatures.
🟢 Correct Answer: D. This reaction is spontaneous at all temperatures.
🔴 Explanation: A reaction with a negative ΔH and a positive ΔS will have a
negative ΔG (ΔG = ΔH - TΔS) at all temperatures. Therefore, it is spontaneous at
all temperatures.
5. What is the maximum number of electrons that can be accommodated in the
third principal energy level (n=3)?
A. 8
B. 18
C. 32
D. 2
, 🟢 Correct Answer: B. 18
🔴 Explanation: The maximum number of electrons in a shell is given by 2n². For
n=3, 2 * 3² = 18 electrons.
6. A solution has a pH of 10. What is the concentration of hydroxide ions [OH-]
in the solution?
A. 1 x 10⁻¹⁰ M
B. 1 x 10⁻⁴ M
C. 1 x 10⁴ M
D. 1 x 10⁻¹⁴ M
🟢 Correct Answer: B. 1 x 10⁻⁴ M
🔴 Explanation: pH + pOH = 14. If pH is 10, pOH is 4. [OH-] = 10^-pOH = 1 x
10⁻⁴ M.
7. A 1.0 M solution of which of the following salts would have the highest pH?
A. NaCl
B. NH4Cl
C. Na2CO3
D. KNO3
🟢 Correct Answer: C. Na2CO3
🔴 Explanation: Na2CO3 is a salt of a strong base (NaOH) and a weak acid
(H2CO3). Its aqueous solution is basic due to the hydrolysis of the carbonate ion,
resulting in the highest pH among the options.
