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 neutral phosphorus atom?
A. 3, 1, –1, –½
B. 3, 2, 0, +½
C. 2, 1, +1, –½
D. 3, 0, 0, +½
Correct Answer: A
Explanation: Phosphorus (Z = 15) ends with the configuration [Ne] 3s² 3p³. The third 3p
electron occupies 3pₓ (m = –1) with spin –½ to obey Hund’s rule.
2. Arrange the following species in order of increasing first-ionization energy: Mg,
Al, Si, Na.
A. Na < Mg < Al < Si
B. Na < Al < Mg < Si
,C. Mg < Na < Al < Si
D. Na < Mg < Si < Al
Correct Answer: B
Explanation: Ionization energy increases across a period. The slight dip between Mg (3s²)
and Al (3p¹) occurs because the 3p electron is farther from the nucleus and experiences
more shielding.
3. How many unpaired electrons are present in the ground-state Lewis symbol of
sulfur?
A. 0
B. 1
C. 2
D. 4
Correct Answer: C
Explanation: Sulfur’s valence configuration is 3s² 3p⁴; the two 3p orbitals each contain
one unpaired electron (Hund’s rule), giving two unpaired valence electrons.
4. Which pair of atoms forms the most polar single bond?
, A. C–H
B. N–O
C. O–F
D. H–F
Correct Answer: D
Explanation: Electronegativity difference ΔEN (H = 2.20, F = 3.98) = 1.78, the largest
listed, producing the greatest bond dipole.
5. The ionic compound formed between calcium and nitrogen has the empirical
formula:
A. CaN
B. Ca₂N
C. Ca₃N₂
D. CaN₂
Correct Answer: C
Explanation: Ca²⁺ and N³⁻ require the lowest whole-number ratio that balances charge: 3
Ca²⁺ (6+) and 2 N³⁻ (6–) → Ca₃N₂.
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 neutral phosphorus atom?
A. 3, 1, –1, –½
B. 3, 2, 0, +½
C. 2, 1, +1, –½
D. 3, 0, 0, +½
Correct Answer: A
Explanation: Phosphorus (Z = 15) ends with the configuration [Ne] 3s² 3p³. The third 3p
electron occupies 3pₓ (m = –1) with spin –½ to obey Hund’s rule.
2. Arrange the following species in order of increasing first-ionization energy: Mg,
Al, Si, Na.
A. Na < Mg < Al < Si
B. Na < Al < Mg < Si
,C. Mg < Na < Al < Si
D. Na < Mg < Si < Al
Correct Answer: B
Explanation: Ionization energy increases across a period. The slight dip between Mg (3s²)
and Al (3p¹) occurs because the 3p electron is farther from the nucleus and experiences
more shielding.
3. How many unpaired electrons are present in the ground-state Lewis symbol of
sulfur?
A. 0
B. 1
C. 2
D. 4
Correct Answer: C
Explanation: Sulfur’s valence configuration is 3s² 3p⁴; the two 3p orbitals each contain
one unpaired electron (Hund’s rule), giving two unpaired valence electrons.
4. Which pair of atoms forms the most polar single bond?
, A. C–H
B. N–O
C. O–F
D. H–F
Correct Answer: D
Explanation: Electronegativity difference ΔEN (H = 2.20, F = 3.98) = 1.78, the largest
listed, producing the greatest bond dipole.
5. The ionic compound formed between calcium and nitrogen has the empirical
formula:
A. CaN
B. Ca₂N
C. Ca₃N₂
D. CaN₂
Correct Answer: C
Explanation: Ca²⁺ and N³⁻ require the lowest whole-number ratio that balances charge: 3
Ca²⁺ (6+) and 2 N³⁻ (6–) → Ca₃N₂.
