ZUMDAHL (CHAPTER 2-21) QUESTIONS AND
CORRECT ANSWERS (VERIFIED ANSWERS) Q&A
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1. What is the correct interpretation of the law of
conservation of mass in a chemical reaction?
A. Mass is created during reactions
B. Mass is destroyed during reactions
C. Total mass of reactants equals total mass of products
D. Mass changes depending on temperature
Rationale: Chemical reactions rearrange atoms but do not
create or destroy them in ordinary reactions.
Correct answer: C
2. Which subatomic particle determines the identity of an
element?
A. Neutron
B. Electron
C. Proton
D. Positron
Rationale: The atomic number (number of protons) defines the
element.
,Correct answer: C
3. What is the correct shape of a molecule with 4 bonding
pairs and no lone pairs (VSEPR theory)?
A. Linear
B. Trigonal planar
C. Tetrahedral
D. Bent
Rationale: Four electron domains arrange themselves in a
tetrahedral geometry.
Correct answer: C
4. Which of the following best describes an endothermic
reaction?
A. Releases heat
B. Absorbs heat
C. Produces light only
D. Has no energy change
Rationale: Endothermic reactions absorb energy from
surroundings.
Correct answer: B
5. What is the molar mass of CO₂?
,A. 28 g/mol
B. 44 g/mol
C. 32 g/mol
D. 12 g/mol
Rationale: C (12) + 2×O (16) = 44 g/mol.
Correct answer: B
6. Which gas law relates pressure and volume at constant
temperature?
A. Charles’s Law
B. Boyle’s Law
C. Avogadro’s Law
D. Dalton’s Law
Rationale: Boyle’s Law states P₁V₁ = P₂V₂.
Correct answer: B
7. What type of bond involves transfer of electrons?
A. Covalent bond
B. Metallic bond
C. Ionic bond
D. Hydrogen bond
Rationale: Ionic bonds form between metals and nonmetals via
electron transfer.
, Correct answer: C
8. What is the pH of a neutral solution at 25°C?
A. 0
B. 7
C. 14
D. 1
Rationale: Neutral water has equal H⁺ and OH⁻ concentrations.
Correct answer: B
9. Which quantum number describes orbital shape?
A. Principal quantum number
B. Magnetic quantum number
C. Spin quantum number
D. Angular momentum quantum number
Rationale: l (angular momentum quantum number) defines
shape (s, p, d, f).
Correct answer: D
10. Which process increases entropy?
A. Freezing water
B. Crystallization