200+ QUESTIONS & ANSWERS WITH
RATIONALES
, WGU D425 Intro to Chemistry Final Exam 2026/2027 | Practice Questions,
Answers & Rationales | OA Prep
Section 1: Matter, Measurement & Atomic Structure (Q1–15)
Question 1
Which of the following is an example of a physical change?
A. Rusting of iron
B. Melting of ice
C. Burning of wood
D. Digesting food
Answer: B
Rationale: Melting is a phase change — no new substance forms, and it's reversible by cooling.
The others involve chemical bonds breaking/forming to create new substances.
Question 2
A sample has a mass of 45.0 g and a volume of 5.0 mL. What is its density?
A. 0.11 g/mL
B. 9.0 g/mL
C. 225 g/mL
D. 50.0 g/mL
Answer: B
Rationale: Density = mass/volume = 45.0 g ÷ 5.0 mL = 9.0 g/mL.
Question 3
How many significant figures are in the measurement 0.004205 g?
,A. 3
B. 4
C. 7
D. 6
Answer: B
Rationale: Leading zeros are never significant. The digits 4, 2, 0, 5 are significant (the zero
between 2 and 5 counts because it's sandwiched between nonzero digits).
Question 4
Which subatomic particle has essentially no mass and a negative charge?
A. Proton
B. Neutron
C. Electron
D. Positron
Answer: C
Rationale: Electrons have a charge of −1 and a mass roughly 1/1836 that of a proton —
negligible compared to protons/neutrons.
Question 5
An atom has 17 protons, 18 neutrons, and 17 electrons. What is its mass number?
A. 17
B. 18
C. 35
D. 52
Answer: C
Rationale: Mass number = protons + neutrons = 17 + 18 = 35.
Question 6
, Isotopes of the same element differ in:
A. Number of protons
B. Number of neutrons
C. Number of electrons
D. Atomic number
Answer: B
Rationale: Isotopes share the same proton count (same element) but have different neutron
counts, giving different mass numbers.
Question 7
What is the electron configuration of a neutral chlorine atom (Z = 17)?
A. 1s² 2s² 2p⁶ 3s² 3p⁴
B. 1s² 2s² 2p⁶ 3s² 3p⁵
C. 1s² 2s² 2p⁶ 3s² 3p⁶
D. 1s² 2s² 2p⁵ 3s² 3p⁶
Answer: B
Rationale: Filling in order (1s, 2s, 2p, 3s, 3p) for 17 electrons gives 2+2+6+2+5 = 17.
Question 8
Which quantum number describes the shape of an orbital?
A. Principal (n)
B. Angular momentum (l)
C. Magnetic (mₗ)
D. Spin (mₛ)
Answer: B
Rationale: The angular momentum (azimuthal) quantum number determines orbital shape — s,
p, d, f.
RATIONALES
, WGU D425 Intro to Chemistry Final Exam 2026/2027 | Practice Questions,
Answers & Rationales | OA Prep
Section 1: Matter, Measurement & Atomic Structure (Q1–15)
Question 1
Which of the following is an example of a physical change?
A. Rusting of iron
B. Melting of ice
C. Burning of wood
D. Digesting food
Answer: B
Rationale: Melting is a phase change — no new substance forms, and it's reversible by cooling.
The others involve chemical bonds breaking/forming to create new substances.
Question 2
A sample has a mass of 45.0 g and a volume of 5.0 mL. What is its density?
A. 0.11 g/mL
B. 9.0 g/mL
C. 225 g/mL
D. 50.0 g/mL
Answer: B
Rationale: Density = mass/volume = 45.0 g ÷ 5.0 mL = 9.0 g/mL.
Question 3
How many significant figures are in the measurement 0.004205 g?
,A. 3
B. 4
C. 7
D. 6
Answer: B
Rationale: Leading zeros are never significant. The digits 4, 2, 0, 5 are significant (the zero
between 2 and 5 counts because it's sandwiched between nonzero digits).
Question 4
Which subatomic particle has essentially no mass and a negative charge?
A. Proton
B. Neutron
C. Electron
D. Positron
Answer: C
Rationale: Electrons have a charge of −1 and a mass roughly 1/1836 that of a proton —
negligible compared to protons/neutrons.
Question 5
An atom has 17 protons, 18 neutrons, and 17 electrons. What is its mass number?
A. 17
B. 18
C. 35
D. 52
Answer: C
Rationale: Mass number = protons + neutrons = 17 + 18 = 35.
Question 6
, Isotopes of the same element differ in:
A. Number of protons
B. Number of neutrons
C. Number of electrons
D. Atomic number
Answer: B
Rationale: Isotopes share the same proton count (same element) but have different neutron
counts, giving different mass numbers.
Question 7
What is the electron configuration of a neutral chlorine atom (Z = 17)?
A. 1s² 2s² 2p⁶ 3s² 3p⁴
B. 1s² 2s² 2p⁶ 3s² 3p⁵
C. 1s² 2s² 2p⁶ 3s² 3p⁶
D. 1s² 2s² 2p⁵ 3s² 3p⁶
Answer: B
Rationale: Filling in order (1s, 2s, 2p, 3s, 3p) for 17 electrons gives 2+2+6+2+5 = 17.
Question 8
Which quantum number describes the shape of an orbital?
A. Principal (n)
B. Angular momentum (l)
C. Magnetic (mₗ)
D. Spin (mₛ)
Answer: B
Rationale: The angular momentum (azimuthal) quantum number determines orbital shape — s,
p, d, f.
