ACS College Chemistry Examination
Questions and Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A | Instant Download Pdf
1. The smallest particle of an element that retains the properties of that
element is a:
A. Molecule
B. Ion
C. Atom
D. Compound
Answer: C. Atom
Rationale: An atom is the basic unit of an element that maintains its chemical
identity.
2. The positively charged particle in an atom is the:
A. Electron
B. Neutron
C. Proton
D. Photon
Answer: C. Proton
Rationale: Protons carry a +1 charge and are located in the nucleus.
3. The particle with no electrical charge is the:
,A. Proton
B. Electron
C. Neutron
D. Ion
Answer: C. Neutron
Rationale: Neutrons are neutral particles found in the atomic nucleus.
4. The atomic number of an element equals the number of:
A. Neutrons
B. Electrons and neutrons
C. Protons
D. Nucleons
Answer: C. Protons
Rationale: The atomic number uniquely identifies an element by its proton count.
5. Isotopes of the same element differ in their number of:
A. Protons
B. Electrons
C. Neutrons
D. Valence shells
Answer: C. Neutrons
Rationale: Isotopes have identical proton numbers but different neutron numbers.
6. The mass number of an atom is the sum of:
A. Electrons and protons
B. Electrons and neutrons
C. Protons and neutrons
D. Protons only
,Answer: C. Protons and neutrons
Rationale: Nearly all atomic mass comes from particles in the nucleus.
7. Electrons occupy regions of space called:
A. Nuclei
B. Shells only
C. Orbitals
D. Isotopes
Answer: C. Orbitals
Rationale: Orbitals describe regions where electrons are most likely found.
8. The maximum number of electrons that can occupy one orbital is:
A. 1
B. 2
C. 4
D. 8
Answer: B. 2
Rationale: According to the Pauli exclusion principle, each orbital holds two
electrons.
9. The electron configuration of a stable noble gas has:
A. No electrons
B. One valence electron
C. A filled valence shell
D. No nucleus
Answer: C. A filled valence shell
Rationale: Noble gases are stable because their outer electron shells are complete.
, 10. Elements in the same group of the periodic table have similar:
A. Atomic masses
B. Numbers of neutrons
C. Chemical properties
D. Physical states only
Answer: C. Chemical properties
Rationale: Elements in the same group have similar valence electron
configurations.
11. The most electronegative element is:
A. Oxygen
B. Chlorine
C. Nitrogen
D. Fluorine
Answer: D. Fluorine
Rationale: Fluorine has the strongest attraction for bonding electrons.
12. Atomic radius generally increases:
A. Left to right across a period
B. Down a group
C. Toward fluorine only
D. Toward noble gases only
Answer: B. Down a group
Rationale: Additional electron shells increase atomic size down a group.
13. Ionization energy is the energy required to:
Questions and Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A | Instant Download Pdf
1. The smallest particle of an element that retains the properties of that
element is a:
A. Molecule
B. Ion
C. Atom
D. Compound
Answer: C. Atom
Rationale: An atom is the basic unit of an element that maintains its chemical
identity.
2. The positively charged particle in an atom is the:
A. Electron
B. Neutron
C. Proton
D. Photon
Answer: C. Proton
Rationale: Protons carry a +1 charge and are located in the nucleus.
3. The particle with no electrical charge is the:
,A. Proton
B. Electron
C. Neutron
D. Ion
Answer: C. Neutron
Rationale: Neutrons are neutral particles found in the atomic nucleus.
4. The atomic number of an element equals the number of:
A. Neutrons
B. Electrons and neutrons
C. Protons
D. Nucleons
Answer: C. Protons
Rationale: The atomic number uniquely identifies an element by its proton count.
5. Isotopes of the same element differ in their number of:
A. Protons
B. Electrons
C. Neutrons
D. Valence shells
Answer: C. Neutrons
Rationale: Isotopes have identical proton numbers but different neutron numbers.
6. The mass number of an atom is the sum of:
A. Electrons and protons
B. Electrons and neutrons
C. Protons and neutrons
D. Protons only
,Answer: C. Protons and neutrons
Rationale: Nearly all atomic mass comes from particles in the nucleus.
7. Electrons occupy regions of space called:
A. Nuclei
B. Shells only
C. Orbitals
D. Isotopes
Answer: C. Orbitals
Rationale: Orbitals describe regions where electrons are most likely found.
8. The maximum number of electrons that can occupy one orbital is:
A. 1
B. 2
C. 4
D. 8
Answer: B. 2
Rationale: According to the Pauli exclusion principle, each orbital holds two
electrons.
9. The electron configuration of a stable noble gas has:
A. No electrons
B. One valence electron
C. A filled valence shell
D. No nucleus
Answer: C. A filled valence shell
Rationale: Noble gases are stable because their outer electron shells are complete.
, 10. Elements in the same group of the periodic table have similar:
A. Atomic masses
B. Numbers of neutrons
C. Chemical properties
D. Physical states only
Answer: C. Chemical properties
Rationale: Elements in the same group have similar valence electron
configurations.
11. The most electronegative element is:
A. Oxygen
B. Chlorine
C. Nitrogen
D. Fluorine
Answer: D. Fluorine
Rationale: Fluorine has the strongest attraction for bonding electrons.
12. Atomic radius generally increases:
A. Left to right across a period
B. Down a group
C. Toward fluorine only
D. Toward noble gases only
Answer: B. Down a group
Rationale: Additional electron shells increase atomic size down a group.
13. Ionization energy is the energy required to:
