CHEM 210 Module 2 Exam (Portage Learning
2025/2026) — 30 High-Level Practice Questions
with 100% Correct Answers
1. Which set of quantum numbers (n, l, m , mₛ) is VALID for the last electron
added to a ground-state phosphorus atom?
A. 3, 1, 1, −½
B. 3, 2, 0, +½
C. 2, 1, −1, +½
D. 4, 0, 0, −½
Correct Answer: A
Explanation: Phosphorus (Z = 15) ends with the configuration … 3s² 3p³. The third p
electron enters 3p with n = 3, l = 1, m = +1 (any of the three p orbitals), mₛ = −½
(Hund’s rule). Option A matches.
2. The first ionization energy of neon is among the highest in the periodic table.
Which statement BEST explains this observation?
A. Neon has a half-filled p subshell.
B. Neon possesses a very small atomic radius.
C. The valence electrons experience a large Zeff and a closed-shell configuration.
D. Neon contains an exactly half-filled 2p set, adding extra stability.
Correct Answer: C
Explanation: Neon (2s² 2p⁶) has a complete n = 2 shell; electrons are held tightly by a
high effective nuclear charge (Zeff) with no easily removed electron, giving the largest IE
in period 2. Closed-shell systems are unusually stable.
3. Arrange the following species in order of INCREASING atomic radius: Mg²⁺, Na⁺,
Ne, F⁻.
, A. Mg²⁺ < Na⁺ < Ne < F⁻
B. F⁻ < Ne < Na⁺ < Mg²⁺
C. Na⁺ < Mg²⁺ < F⁻ < Ne
D. Ne < Mg²⁺ < Na⁺ < F⁻
Correct Answer: A
Explanation: All are isoelectronic (10 e⁻). Radius decreases as Z increases because greater
nuclear charge pulls electrons closer. Z values: F (9), Ne (10), Na (11), Mg (12); thus F⁻
largest, Mg²⁺ smallest.
4. How many unpaired electrons are present in the ground-state Lewis-dot symbol
for sulfur?
A. 0
B. 1
C. 2
D. 4
Correct Answer: C
Explanation: Sulfur’s valence config is 3s² 3p⁴; the p subshell contains two orbitals each
with one electron (Hund’s rule), giving two unpaired electrons shown as two single dots
in the Lewis symbol.
5. Which periodic trend is correctly described?
A. Electronegativity increases down a group.
B. Atomic radius decreases across a period (left → right).
C. Ionization energy decreases across a period.
D. Metallic character increases across a period.
Correct Answer: B
Explanation: Adding protons across a period contracts the cloud because Zeff rises while
shell number stays the same; radius therefore decreases.
2025/2026) — 30 High-Level Practice Questions
with 100% Correct Answers
1. Which set of quantum numbers (n, l, m , mₛ) is VALID for the last electron
added to a ground-state phosphorus atom?
A. 3, 1, 1, −½
B. 3, 2, 0, +½
C. 2, 1, −1, +½
D. 4, 0, 0, −½
Correct Answer: A
Explanation: Phosphorus (Z = 15) ends with the configuration … 3s² 3p³. The third p
electron enters 3p with n = 3, l = 1, m = +1 (any of the three p orbitals), mₛ = −½
(Hund’s rule). Option A matches.
2. The first ionization energy of neon is among the highest in the periodic table.
Which statement BEST explains this observation?
A. Neon has a half-filled p subshell.
B. Neon possesses a very small atomic radius.
C. The valence electrons experience a large Zeff and a closed-shell configuration.
D. Neon contains an exactly half-filled 2p set, adding extra stability.
Correct Answer: C
Explanation: Neon (2s² 2p⁶) has a complete n = 2 shell; electrons are held tightly by a
high effective nuclear charge (Zeff) with no easily removed electron, giving the largest IE
in period 2. Closed-shell systems are unusually stable.
3. Arrange the following species in order of INCREASING atomic radius: Mg²⁺, Na⁺,
Ne, F⁻.
, A. Mg²⁺ < Na⁺ < Ne < F⁻
B. F⁻ < Ne < Na⁺ < Mg²⁺
C. Na⁺ < Mg²⁺ < F⁻ < Ne
D. Ne < Mg²⁺ < Na⁺ < F⁻
Correct Answer: A
Explanation: All are isoelectronic (10 e⁻). Radius decreases as Z increases because greater
nuclear charge pulls electrons closer. Z values: F (9), Ne (10), Na (11), Mg (12); thus F⁻
largest, Mg²⁺ smallest.
4. How many unpaired electrons are present in the ground-state Lewis-dot symbol
for sulfur?
A. 0
B. 1
C. 2
D. 4
Correct Answer: C
Explanation: Sulfur’s valence config is 3s² 3p⁴; the p subshell contains two orbitals each
with one electron (Hund’s rule), giving two unpaired electrons shown as two single dots
in the Lewis symbol.
5. Which periodic trend is correctly described?
A. Electronegativity increases down a group.
B. Atomic radius decreases across a period (left → right).
C. Ionization energy decreases across a period.
D. Metallic character increases across a period.
Correct Answer: B
Explanation: Adding protons across a period contracts the cloud because Zeff rises while
shell number stays the same; radius therefore decreases.
