ACS Introductory Chemistry
Examination Questions and Correct
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Rationales 2026 Q&A | Instant
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1. Which state of matter has a definite shape and definite volume?
A. Gas
B. Liquid
C. Plasma
D. Solid
Answer: D. Solid
Rationale: Solids have particles held closely together in fixed positions, giving
them a definite shape and volume.
2. Which state of matter has a definite volume but takes the shape of its
container?
A. Solid
B. Gas
C. Plasma
D. Liquid
Answer: D. Liquid
Rationale: Liquids maintain their volume but flow to match the shape of their
container.
,3. Which state of matter has no definite shape or volume?
A. Solid
B. Liquid
C. Gas
D. Crystal
Answer: C. Gas
Rationale: Gas particles are widely spaced and expand to fill any container.
4. A physical change is a change that
A. Produces a new substance
B. Changes chemical identity
C. Forms new bonds
D. Changes form but not composition
Answer: D. Changes form but not composition
Rationale: Physical changes alter appearance or state without creating a new
substance.
5. Which is an example of a chemical change?
A. Melting ice
B. Cutting paper
C. Boiling water
D. Rusting iron
Answer: D. Rusting iron
Rationale: Rusting produces a new substance, iron oxide, through a chemical
reaction.
6. The smallest unit of an element that retains its properties is a
,A. Molecule
B. Compound
C. Ion
D. Atom
Answer: D. Atom
Rationale: Atoms are the basic units of elements that maintain their chemical
identity.
7. The nucleus of an atom contains
A. Electrons only
B. Neutrons only
C. Electrons and neutrons
D. Protons and neutrons
Answer: D. Protons and neutrons
Rationale: The nucleus contains positively charged protons and neutral neutrons.
8. Which particle has a negative charge?
A. Proton
B. Neutron
C. Nucleus
D. Electron
Answer: D. Electron
Rationale: Electrons carry a negative electrical charge.
9. The atomic number of an element equals the number of
A. Neutrons
B. Electrons plus neutrons
, C. Isotopes
D. Protons
Answer: D. Protons
Rationale: The number of protons identifies the element and defines its atomic
number.
10. Isotopes of an element differ in the number of
A. Protons
B. Electrons
C. Chemical symbols
D. Neutrons
Answer: D. Neutrons
Rationale: Isotopes have the same number of protons but different numbers of
neutrons.
11. The mass number of an atom equals
A. Protons only
B. Electrons only
C. Neutrons only
D. Protons plus neutrons
Answer: D. Protons plus neutrons
Rationale: Mass number represents the total number of particles in the nucleus.
12. A positively charged ion is called a
A. Anion
B. Isotope
C. Molecule
D. Cation
Examination Questions and Correct
Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant
Download Pdf
1. Which state of matter has a definite shape and definite volume?
A. Gas
B. Liquid
C. Plasma
D. Solid
Answer: D. Solid
Rationale: Solids have particles held closely together in fixed positions, giving
them a definite shape and volume.
2. Which state of matter has a definite volume but takes the shape of its
container?
A. Solid
B. Gas
C. Plasma
D. Liquid
Answer: D. Liquid
Rationale: Liquids maintain their volume but flow to match the shape of their
container.
,3. Which state of matter has no definite shape or volume?
A. Solid
B. Liquid
C. Gas
D. Crystal
Answer: C. Gas
Rationale: Gas particles are widely spaced and expand to fill any container.
4. A physical change is a change that
A. Produces a new substance
B. Changes chemical identity
C. Forms new bonds
D. Changes form but not composition
Answer: D. Changes form but not composition
Rationale: Physical changes alter appearance or state without creating a new
substance.
5. Which is an example of a chemical change?
A. Melting ice
B. Cutting paper
C. Boiling water
D. Rusting iron
Answer: D. Rusting iron
Rationale: Rusting produces a new substance, iron oxide, through a chemical
reaction.
6. The smallest unit of an element that retains its properties is a
,A. Molecule
B. Compound
C. Ion
D. Atom
Answer: D. Atom
Rationale: Atoms are the basic units of elements that maintain their chemical
identity.
7. The nucleus of an atom contains
A. Electrons only
B. Neutrons only
C. Electrons and neutrons
D. Protons and neutrons
Answer: D. Protons and neutrons
Rationale: The nucleus contains positively charged protons and neutral neutrons.
8. Which particle has a negative charge?
A. Proton
B. Neutron
C. Nucleus
D. Electron
Answer: D. Electron
Rationale: Electrons carry a negative electrical charge.
9. The atomic number of an element equals the number of
A. Neutrons
B. Electrons plus neutrons
, C. Isotopes
D. Protons
Answer: D. Protons
Rationale: The number of protons identifies the element and defines its atomic
number.
10. Isotopes of an element differ in the number of
A. Protons
B. Electrons
C. Chemical symbols
D. Neutrons
Answer: D. Neutrons
Rationale: Isotopes have the same number of protons but different numbers of
neutrons.
11. The mass number of an atom equals
A. Protons only
B. Electrons only
C. Neutrons only
D. Protons plus neutrons
Answer: D. Protons plus neutrons
Rationale: Mass number represents the total number of particles in the nucleus.
12. A positively charged ion is called a
A. Anion
B. Isotope
C. Molecule
D. Cation
