1
CHEM 210 - PRACTICE EXAM 2026/2027 |
EXAM PREP | 150 VERIFIED Q&A | DETAILED
RATIONALES | NGN-ALIGNED | PASS
GUARANTEED – A+ GRADED
SECTION I: ATOMIC STRUCTURE AND PERIODICITY - Questions 1-15
Q1: Atomic number
The student is reviewing atomic structure. What does the atomic number of an element
represent?
A. Number of neutrons
B. Number of protons
C. Number of electrons
D. Mass number
Correct Answer: B
Rationale: The atomic number (Z) equals the number of protons in the nucleus. It defines the
element's identity. In a neutral atom, electrons equal protons, but the atomic number itself
refers only to protons. [100% CORRECT]
Q2: Isotopes
The student is reviewing isotopes. What are isotopes?
A. Atoms of the same element with different numbers of protons
B. Atoms of the same element with different numbers of neutrons
C. Atoms with different numbers of electrons
D. Ions with a positive charge
Correct Answer: B
Rationale: Isotopes are atoms of the same element that have the same number of protons but
different numbers of neutrons, resulting in different mass numbers. [100% CORRECT]
Q3: Electron configuration
The student is reviewing electron configuration. What is the electron configuration of oxygen (Z
= 8)?
A. 1s² 2s² 2p⁴
B. 1s² 2s² 2p⁶
,2
C. 1s² 2s² 2p³
D. 1s² 2s² 2p⁵
Correct Answer: A
Rationale: Oxygen has 8 electrons: 2 in 1s, 2 in 2s, and 4 in 2p. Therefore, 1s² 2s² 2p⁴. [100%
CORRECT]
Q4: Periodic trend: atomic radius
The student is reviewing periodic trends. How does atomic radius change across a period from
left to right?
A. Increases
B. Decreases
C. Remains constant
D. Increases then decreases
Correct Answer: B
Rationale: Across a period, increasing nuclear charge pulls electrons closer, so atomic radius
generally decreases from left to right. Down a group, radius increases due to additional electron
shells. [100% CORRECT]
Q5: Periodic trend: ionization energy
The student is reviewing periodic trends. How does first ionization energy change down a
group?
A. Increases
B. Decreases
C. Remains constant
D. Randomly fluctuates
Correct Answer: B
Rationale: Down a group, valence electrons are farther from the nucleus and shielded by inner
electrons, so ionization energy decreases. Across a period, it generally increases. [100%
CORRECT]
Q6: Electronegativity
The student is reviewing electronegativity. Which element has the highest electronegativity?
A. Fluorine
B. Oxygen
C. Chlorine
D. Nitrogen
,3
Correct Answer: A
Rationale: Fluorine is the most electronegative element (Pauling scale ~4.0). Electronegativity
increases across a period and decreases down a group. [100% CORRECT]
Q7: Quantum numbers
The student is reviewing quantum numbers. What does the principal quantum number (n)
indicate?
A. Orbital shape
B. Orbital orientation
C. Electron spin
D. Principal energy level and size
Correct Answer: D
Rationale: The principal quantum number n indicates the main energy level (shell) and relative
size of the orbital. It takes positive integer values (1, 2, 3, ...). [100% CORRECT]
Q8: Orbital shapes
The student is reviewing atomic orbitals. What is the shape of an s orbital?
A. Spherical
B. Dumbbell-shaped
C. Cloverleaf-shaped
D. Complex
Correct Answer: A
Rationale: s orbitals are spherical. p orbitals are dumbbell-shaped, and d orbitals are generally
cloverleaf-shaped or more complex. [100% CORRECT]
Q9: Hund's rule
The student is reviewing electron filling. What does Hund's rule state?
A. Electrons fill orbitals of lowest energy first
B. Each orbital can hold a maximum of two electrons
C. Electrons occupy degenerate orbitals singly before pairing
D. Electrons pair before occupying empty orbitals
Correct Answer: C
Rationale: Hund's rule: For degenerate orbitals (same energy), electrons occupy them singly
with parallel spins before pairing. This minimizes electron-electron repulsion. [100% CORRECT]
Q10: Pauli exclusion principle
The student is reviewing quantum mechanics. What does the Pauli exclusion principle state?
, 4
A. No two electrons in an atom can have the same four quantum numbers
B. Electrons fill lowest energy orbitals first
C. Electrons occupy degenerate orbitals singly
D. Electrons have both wave and particle properties
Correct Answer: A
Rationale: The Pauli exclusion principle states that no two electrons in the same atom can have
identical sets of all four quantum numbers (n, l, ml, ms). This limits each orbital to two electrons
with opposite spins. [100% CORRECT]
Q11: Effective nuclear charge
The student is reviewing periodic trends. How does effective nuclear charge (Zeff) change across
a period?
A. Increases
B. Decreases
C. Remains constant
D. Randomly fluctuates
Correct Answer: A
Rationale: Across a period, protons are added to the nucleus while electrons enter the same
shell, so shielding changes little. Zeff increases, pulling electrons closer. [100% CORRECT]
Q12: Ionic radii
The student is reviewing ionic radii. Which ion is larger than its neutral atom?
A. Na⁺
B. Mg²⁺
C. Cl⁻
D. Al³⁺
Correct Answer: C
Rationale: Anions are larger than their neutral atoms because added electrons increase
repulsion. Cl⁻ is larger than Cl. Cations are smaller. [100% CORRECT]
Q13: Magnetic properties
The student is reviewing magnetism. Which ion is paramagnetic?
A. Zn²⁺
B. Cu²⁺
C. Ca²⁺
D. Sc³⁺
CHEM 210 - PRACTICE EXAM 2026/2027 |
EXAM PREP | 150 VERIFIED Q&A | DETAILED
RATIONALES | NGN-ALIGNED | PASS
GUARANTEED – A+ GRADED
SECTION I: ATOMIC STRUCTURE AND PERIODICITY - Questions 1-15
Q1: Atomic number
The student is reviewing atomic structure. What does the atomic number of an element
represent?
A. Number of neutrons
B. Number of protons
C. Number of electrons
D. Mass number
Correct Answer: B
Rationale: The atomic number (Z) equals the number of protons in the nucleus. It defines the
element's identity. In a neutral atom, electrons equal protons, but the atomic number itself
refers only to protons. [100% CORRECT]
Q2: Isotopes
The student is reviewing isotopes. What are isotopes?
A. Atoms of the same element with different numbers of protons
B. Atoms of the same element with different numbers of neutrons
C. Atoms with different numbers of electrons
D. Ions with a positive charge
Correct Answer: B
Rationale: Isotopes are atoms of the same element that have the same number of protons but
different numbers of neutrons, resulting in different mass numbers. [100% CORRECT]
Q3: Electron configuration
The student is reviewing electron configuration. What is the electron configuration of oxygen (Z
= 8)?
A. 1s² 2s² 2p⁴
B. 1s² 2s² 2p⁶
,2
C. 1s² 2s² 2p³
D. 1s² 2s² 2p⁵
Correct Answer: A
Rationale: Oxygen has 8 electrons: 2 in 1s, 2 in 2s, and 4 in 2p. Therefore, 1s² 2s² 2p⁴. [100%
CORRECT]
Q4: Periodic trend: atomic radius
The student is reviewing periodic trends. How does atomic radius change across a period from
left to right?
A. Increases
B. Decreases
C. Remains constant
D. Increases then decreases
Correct Answer: B
Rationale: Across a period, increasing nuclear charge pulls electrons closer, so atomic radius
generally decreases from left to right. Down a group, radius increases due to additional electron
shells. [100% CORRECT]
Q5: Periodic trend: ionization energy
The student is reviewing periodic trends. How does first ionization energy change down a
group?
A. Increases
B. Decreases
C. Remains constant
D. Randomly fluctuates
Correct Answer: B
Rationale: Down a group, valence electrons are farther from the nucleus and shielded by inner
electrons, so ionization energy decreases. Across a period, it generally increases. [100%
CORRECT]
Q6: Electronegativity
The student is reviewing electronegativity. Which element has the highest electronegativity?
A. Fluorine
B. Oxygen
C. Chlorine
D. Nitrogen
,3
Correct Answer: A
Rationale: Fluorine is the most electronegative element (Pauling scale ~4.0). Electronegativity
increases across a period and decreases down a group. [100% CORRECT]
Q7: Quantum numbers
The student is reviewing quantum numbers. What does the principal quantum number (n)
indicate?
A. Orbital shape
B. Orbital orientation
C. Electron spin
D. Principal energy level and size
Correct Answer: D
Rationale: The principal quantum number n indicates the main energy level (shell) and relative
size of the orbital. It takes positive integer values (1, 2, 3, ...). [100% CORRECT]
Q8: Orbital shapes
The student is reviewing atomic orbitals. What is the shape of an s orbital?
A. Spherical
B. Dumbbell-shaped
C. Cloverleaf-shaped
D. Complex
Correct Answer: A
Rationale: s orbitals are spherical. p orbitals are dumbbell-shaped, and d orbitals are generally
cloverleaf-shaped or more complex. [100% CORRECT]
Q9: Hund's rule
The student is reviewing electron filling. What does Hund's rule state?
A. Electrons fill orbitals of lowest energy first
B. Each orbital can hold a maximum of two electrons
C. Electrons occupy degenerate orbitals singly before pairing
D. Electrons pair before occupying empty orbitals
Correct Answer: C
Rationale: Hund's rule: For degenerate orbitals (same energy), electrons occupy them singly
with parallel spins before pairing. This minimizes electron-electron repulsion. [100% CORRECT]
Q10: Pauli exclusion principle
The student is reviewing quantum mechanics. What does the Pauli exclusion principle state?
, 4
A. No two electrons in an atom can have the same four quantum numbers
B. Electrons fill lowest energy orbitals first
C. Electrons occupy degenerate orbitals singly
D. Electrons have both wave and particle properties
Correct Answer: A
Rationale: The Pauli exclusion principle states that no two electrons in the same atom can have
identical sets of all four quantum numbers (n, l, ml, ms). This limits each orbital to two electrons
with opposite spins. [100% CORRECT]
Q11: Effective nuclear charge
The student is reviewing periodic trends. How does effective nuclear charge (Zeff) change across
a period?
A. Increases
B. Decreases
C. Remains constant
D. Randomly fluctuates
Correct Answer: A
Rationale: Across a period, protons are added to the nucleus while electrons enter the same
shell, so shielding changes little. Zeff increases, pulling electrons closer. [100% CORRECT]
Q12: Ionic radii
The student is reviewing ionic radii. Which ion is larger than its neutral atom?
A. Na⁺
B. Mg²⁺
C. Cl⁻
D. Al³⁺
Correct Answer: C
Rationale: Anions are larger than their neutral atoms because added electrons increase
repulsion. Cl⁻ is larger than Cl. Cations are smaller. [100% CORRECT]
Q13: Magnetic properties
The student is reviewing magnetism. Which ion is paramagnetic?
A. Zn²⁺
B. Cu²⁺
C. Ca²⁺
D. Sc³⁺
