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 an electron in a
ground-state arsenic atom?
A. 3, 3, 0, +½
B. 4, 2, –1, –½
C. 4, 1, 2, +½
D. 3, 2, –3, –½
Correct Answer: B
Short Explanation: l must be ≤ n – 1; for n = 4, l = 2 (d orbital) is allowed, m = –1 is
within –l…+l, and mₛ = ±½. Option A violates l ≤ n – 1; C has |m | > l; D has |m | > l.
2. The first ionization energy of aluminum is lower than that of magnesium because:
A. Al has a smaller atomic radius
B. Al’s outer electron occupies a higher-energy subshell
C. Al has a greater nuclear charge
D. Al contains more neutrons
Correct Answer: B
Short Explanation: Al’s 3p electron is farther from the nucleus and less tightly held than
Mg’s 3s electron, despite greater Z; radius is actually larger, and neutron count does not
affect ionization energy.
, 3. How many unpaired electrons are in a ground-state Mo atom (Z = 42)?
A. 4
B. 5
C. 6
D. 7
Correct Answer: C
Short Explanation: [Kr] 5s¹ 4d⁵ (half-filled d stability); five d electrons plus one s
electron give six unpaired.
4. 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
Short Explanation: Isoelectronic with Ne (10 e⁻); radius decreases as nuclear charge
increases (F⁻ 9, Ne 10, Na⁺ 11, Mg²⁺ 12).
5. Which orbital designation corresponds to n = 5, l = 3?
A. 5p
B. 5d
C. 5f
D. 5g
Correct Answer: C
2025/2026) — 30 High-Level Practice Questions
with 100% Correct Answers
1. Which set of quantum numbers (n, l, m , mₛ) is valid for an electron in a
ground-state arsenic atom?
A. 3, 3, 0, +½
B. 4, 2, –1, –½
C. 4, 1, 2, +½
D. 3, 2, –3, –½
Correct Answer: B
Short Explanation: l must be ≤ n – 1; for n = 4, l = 2 (d orbital) is allowed, m = –1 is
within –l…+l, and mₛ = ±½. Option A violates l ≤ n – 1; C has |m | > l; D has |m | > l.
2. The first ionization energy of aluminum is lower than that of magnesium because:
A. Al has a smaller atomic radius
B. Al’s outer electron occupies a higher-energy subshell
C. Al has a greater nuclear charge
D. Al contains more neutrons
Correct Answer: B
Short Explanation: Al’s 3p electron is farther from the nucleus and less tightly held than
Mg’s 3s electron, despite greater Z; radius is actually larger, and neutron count does not
affect ionization energy.
, 3. How many unpaired electrons are in a ground-state Mo atom (Z = 42)?
A. 4
B. 5
C. 6
D. 7
Correct Answer: C
Short Explanation: [Kr] 5s¹ 4d⁵ (half-filled d stability); five d electrons plus one s
electron give six unpaired.
4. 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
Short Explanation: Isoelectronic with Ne (10 e⁻); radius decreases as nuclear charge
increases (F⁻ 9, Ne 10, Na⁺ 11, Mg²⁺ 12).
5. Which orbital designation corresponds to n = 5, l = 3?
A. 5p
B. 5d
C. 5f
D. 5g
Correct Answer: C
