WGU C165 CHEMISTRY OA EXAM (2026
EDITION) – PHYSICAL SCIENCE 200
Questions | Answers & Rationales
Exam Blueprint:
Atomic Structure & Periodic Table (20%) – 40 Qs
Chemical Bonding & Molecular Structure (15%) – 30 Qs
Chemical Reactions & Equations (20%) – 40 Qs
Stoichiometry & Mole Concept (15%) – 30 Qs
States of Matter & Solutions (15%) – 30 Qs
Acids, Bases & Nuclear Chemistry (15%) – 30 Qs
Time limit (simulated): 2.5 hours (0.75 min/question)
Passing threshold: 70% (140/200)
SECTION 1: ATOMIC STRUCTURE & PERIODIC TABLE (Questions 1–40)
1. The three main subatomic particles are:
A) Protons, neutrons, electrons
B) Protons, isotopes, ions
C) Positrons, neutrons, electrons
D) Alpha, beta, gamma
Answer: A
,Rationale: Atoms are composed of protons (+), neutrons (neutral), and
electrons (−). Protons and neutrons are in the nucleus.
2. Which subatomic particle has a positive charge?
A) Proton
B) Neutron
C) Electron
D) Positron
Answer: A
Rationale: Protons have a charge of +1; electrons are −1; neutrons are
neutral.
3. Which subatomic particle determines the identity of an element (atomic
number)?
A) Number of protons
B) Number of neutrons
C) Number of electrons
D) Total mass
Answer: A
Rationale: The atomic number (Z) is the number of protons; elements differ
by proton count.
4. The mass number of an atom is the sum of:
A) Protons and neutrons
B) Protons and electrons
,C) Neutrons and electrons
D) Protons, neutrons, and electrons
Answer: A
Rationale: Mass number = protons + neutrons. Electrons have negligible
mass.
5. Isotopes are atoms with the same number of protons but different
numbers of:
A) Neutrons
B) Electrons
C) Positrons
D) Quarks
Answer: A
Rationale: Isotopes have the same atomic number (Z) but different mass
numbers (A) due to differing neutron counts.
6. Carbon-12, carbon-13, and carbon-14 are examples of:
A) Isotopes
B) Ions
C) Allotropes
D) Isomers
Answer: A
Rationale: All have 6 protons but 6, 7, and 8 neutrons respectively.
7. An atom that gains or loses electrons becomes a(n):
A) Isotope
, B) Ion
C) Molecule
D) Compound
Answer: B
Rationale: Cations (loss of electrons) are positively charged; anions (gain of
electrons) are negatively charged.
8. Na⁺ is an example of:
A) A cation (positive ion)
B) An anion
C) An isotope
D) A molecule
Answer: A
Rationale: Sodium loses one electron to become Na⁺, a cation.
9. The nucleus of an atom contains:
A) Protons and neutrons
B) Protons and electrons
C) Neutrons and electrons
D) Only neutrons
Answer: A
Rationale: The nucleus is dense and positively charged, containing protons
and neutrons; electrons orbit the nucleus.
10. The electron cloud model describes:
EDITION) – PHYSICAL SCIENCE 200
Questions | Answers & Rationales
Exam Blueprint:
Atomic Structure & Periodic Table (20%) – 40 Qs
Chemical Bonding & Molecular Structure (15%) – 30 Qs
Chemical Reactions & Equations (20%) – 40 Qs
Stoichiometry & Mole Concept (15%) – 30 Qs
States of Matter & Solutions (15%) – 30 Qs
Acids, Bases & Nuclear Chemistry (15%) – 30 Qs
Time limit (simulated): 2.5 hours (0.75 min/question)
Passing threshold: 70% (140/200)
SECTION 1: ATOMIC STRUCTURE & PERIODIC TABLE (Questions 1–40)
1. The three main subatomic particles are:
A) Protons, neutrons, electrons
B) Protons, isotopes, ions
C) Positrons, neutrons, electrons
D) Alpha, beta, gamma
Answer: A
,Rationale: Atoms are composed of protons (+), neutrons (neutral), and
electrons (−). Protons and neutrons are in the nucleus.
2. Which subatomic particle has a positive charge?
A) Proton
B) Neutron
C) Electron
D) Positron
Answer: A
Rationale: Protons have a charge of +1; electrons are −1; neutrons are
neutral.
3. Which subatomic particle determines the identity of an element (atomic
number)?
A) Number of protons
B) Number of neutrons
C) Number of electrons
D) Total mass
Answer: A
Rationale: The atomic number (Z) is the number of protons; elements differ
by proton count.
4. The mass number of an atom is the sum of:
A) Protons and neutrons
B) Protons and electrons
,C) Neutrons and electrons
D) Protons, neutrons, and electrons
Answer: A
Rationale: Mass number = protons + neutrons. Electrons have negligible
mass.
5. Isotopes are atoms with the same number of protons but different
numbers of:
A) Neutrons
B) Electrons
C) Positrons
D) Quarks
Answer: A
Rationale: Isotopes have the same atomic number (Z) but different mass
numbers (A) due to differing neutron counts.
6. Carbon-12, carbon-13, and carbon-14 are examples of:
A) Isotopes
B) Ions
C) Allotropes
D) Isomers
Answer: A
Rationale: All have 6 protons but 6, 7, and 8 neutrons respectively.
7. An atom that gains or loses electrons becomes a(n):
A) Isotope
, B) Ion
C) Molecule
D) Compound
Answer: B
Rationale: Cations (loss of electrons) are positively charged; anions (gain of
electrons) are negatively charged.
8. Na⁺ is an example of:
A) A cation (positive ion)
B) An anion
C) An isotope
D) A molecule
Answer: A
Rationale: Sodium loses one electron to become Na⁺, a cation.
9. The nucleus of an atom contains:
A) Protons and neutrons
B) Protons and electrons
C) Neutrons and electrons
D) Only neutrons
Answer: A
Rationale: The nucleus is dense and positively charged, containing protons
and neutrons; electrons orbit the nucleus.
10. The electron cloud model describes:
