CHEM134 Midterm Exam Practice
Questions And Correct Answers
(Verified Answers) Plus Rationale 2026
Q&A| Instant Download Pdf
1. Which statement best describes the law of conservation of mass
during a chemical reaction?
A. Mass is converted completely into energy.
B. The total mass of reactants always equals the total mass of products
in a closed system.
C. Products always weigh more than reactants.
D. Atoms disappear during combustion.
B. The total mass of reactants always equals the total mass of
products in a closed system.
Rationale: The law of conservation of mass states that matter is neither
created nor destroyed during ordinary chemical reactions. In a closed
system, the total mass remains constant because atoms are simply
rearranged.
2. Which of the following best distinguishes an element from a
compound?
A. An element can be separated into simpler substances by chemical
means.
B. A compound contains only one type of atom.
C. An element consists of only one type of atom, whereas a
, compound contains two or more chemically combined elements.
D. A compound is always a gas.
Rationale: Elements are pure substances composed of one kind of
atom, while compounds consist of chemically bonded atoms of
different elements in fixed proportions.
3. What is the atomic number of an element?
A. Total number of protons and neutrons
B. Number of protons in the nucleus
C. Number of neutrons only
D. Number of electrons and neutrons
Rationale: The atomic number uniquely identifies an element
because it equals the number of protons in its nucleus.
4. Which subatomic particle has a negative charge?
A. Proton
B. Electron
C. Neutron
D. Alpha particle
Rationale: Electrons carry a negative charge, protons are positively
charged, and neutrons are electrically neutral.
5. Which type of bond results from the sharing of electrons?
A. Ionic bond
B. Covalent bond
C. Metallic bond
D. Hydrogen bond
Rationale: Covalent bonds form when atoms share electron pairs to
achieve greater stability.
6. Sodium chloride is classified as a:
A. Molecular compound
B. Ionic compound
, C. Metallic alloy
D. Pure element
Rationale: Sodium chloride forms through electron transfer between
sodium and chlorine, producing oppositely charged ions held
together by electrostatic attraction.
7. Which orbital is filled before electrons occupy the 3p orbital?
A. 4s
B. 3s
C. 2d
D. 3d
Rationale: According to the Aufbau principle, electrons fill lower-
energy orbitals first, placing the 3s orbital before the 3p orbital.
8. Which quantum number describes the shape of an orbital?
A. Principal quantum number
B. Angular momentum quantum number
C. Magnetic quantum number
D. Spin quantum number
Rationale: The angular momentum (azimuthal) quantum number
determines the subshell and orbital shape.
9. Which periodic trend generally increases from left to right across a
period?
A. Atomic radius
B. Ionization energy
C. Metallic character
D. Shielding effect
Rationale: Ionization energy generally increases across a period
because effective nuclear charge increases, making electrons more
difficult to remove.
Questions And Correct Answers
(Verified Answers) Plus Rationale 2026
Q&A| Instant Download Pdf
1. Which statement best describes the law of conservation of mass
during a chemical reaction?
A. Mass is converted completely into energy.
B. The total mass of reactants always equals the total mass of products
in a closed system.
C. Products always weigh more than reactants.
D. Atoms disappear during combustion.
B. The total mass of reactants always equals the total mass of
products in a closed system.
Rationale: The law of conservation of mass states that matter is neither
created nor destroyed during ordinary chemical reactions. In a closed
system, the total mass remains constant because atoms are simply
rearranged.
2. Which of the following best distinguishes an element from a
compound?
A. An element can be separated into simpler substances by chemical
means.
B. A compound contains only one type of atom.
C. An element consists of only one type of atom, whereas a
, compound contains two or more chemically combined elements.
D. A compound is always a gas.
Rationale: Elements are pure substances composed of one kind of
atom, while compounds consist of chemically bonded atoms of
different elements in fixed proportions.
3. What is the atomic number of an element?
A. Total number of protons and neutrons
B. Number of protons in the nucleus
C. Number of neutrons only
D. Number of electrons and neutrons
Rationale: The atomic number uniquely identifies an element
because it equals the number of protons in its nucleus.
4. Which subatomic particle has a negative charge?
A. Proton
B. Electron
C. Neutron
D. Alpha particle
Rationale: Electrons carry a negative charge, protons are positively
charged, and neutrons are electrically neutral.
5. Which type of bond results from the sharing of electrons?
A. Ionic bond
B. Covalent bond
C. Metallic bond
D. Hydrogen bond
Rationale: Covalent bonds form when atoms share electron pairs to
achieve greater stability.
6. Sodium chloride is classified as a:
A. Molecular compound
B. Ionic compound
, C. Metallic alloy
D. Pure element
Rationale: Sodium chloride forms through electron transfer between
sodium and chlorine, producing oppositely charged ions held
together by electrostatic attraction.
7. Which orbital is filled before electrons occupy the 3p orbital?
A. 4s
B. 3s
C. 2d
D. 3d
Rationale: According to the Aufbau principle, electrons fill lower-
energy orbitals first, placing the 3s orbital before the 3p orbital.
8. Which quantum number describes the shape of an orbital?
A. Principal quantum number
B. Angular momentum quantum number
C. Magnetic quantum number
D. Spin quantum number
Rationale: The angular momentum (azimuthal) quantum number
determines the subshell and orbital shape.
9. Which periodic trend generally increases from left to right across a
period?
A. Atomic radius
B. Ionization energy
C. Metallic character
D. Shielding effect
Rationale: Ionization energy generally increases across a period
because effective nuclear charge increases, making electrons more
difficult to remove.
