CHEM 210 Module 2 Exam (Portage Learning
2025/2026) — 30 High-Level Practice Questions with
100% Correct Answers
1. How many protons, neutrons, and electrons are in a neutral atom of ⁶⁵₂₉Cu?
A. 29 p⁺, 34 n°, 29 e⁻
B. 34 p⁺, 29 n°, 34 e⁻
C. 29 p⁺, 35 n°, 29 e⁻
D. 30 p⁺, 35 n°, 30 e⁻
Correct Answer: A
Explanation: Atomic number (29) = protons = electrons in a neutral atom. Mass number
(65) – atomic number = 65 – 29 = 34 neutrons.
2. Which quantum-number set is valid for the last electron added to a neutral
phosphorus atom (Z = 15)?
A. n = 3, l = 2, m = 0, mₛ = +½
B. n = 3, l = 1, m = –1, mₛ = +½
,C. n = 2, l = 1, m = 0, mₛ = –½
D. n = 4, l = 0, m = 0, mₛ = +½
Correct Answer: B
Explanation: Phosphorus ends with 3p³; the third 3p electron enters one of the degenerate
3p orbitals with m = –1, 0, or +1 and parallel spin (Hund’s rule). All values are within
allowed ranges.
3. Arrange the following species in order of increasing first-ionization energy: Mg,
Al, Na, Si.
A. Na < Mg < Al < Si
B. Mg < Na < Al < Si
C. Na < Al < Mg < Si
D. Si < Al < Mg < Na
Correct Answer: A
Explanation: Ionization energy increases left-to-right across a period; Na (period 3, group
1) is lowest, followed by Mg, Al, and Si highest.
4. Which element has the largest atomic radius among S, Cl, Se, and Br?
, A. S
B. Cl
C. Se
D. Br
Correct Answer: D
Explanation: Atomic radius increases down a group and left-to-right across a period. Br is
below Cl in group 17 and below Se in period 4, giving it the largest radius.
5. How many unpaired electrons are present in a ground-state sulfur atom (Z = 16)?
A. 0
B. 1
C. 2
D. 3
Correct Answer: C
Explanation: Sulfur’s configuration is 1s² 2s² 2p⁶ 3s² 3p⁴; the 3p subshell contains two
unpaired electrons (Hund’s rule).
2025/2026) — 30 High-Level Practice Questions with
100% Correct Answers
1. How many protons, neutrons, and electrons are in a neutral atom of ⁶⁵₂₉Cu?
A. 29 p⁺, 34 n°, 29 e⁻
B. 34 p⁺, 29 n°, 34 e⁻
C. 29 p⁺, 35 n°, 29 e⁻
D. 30 p⁺, 35 n°, 30 e⁻
Correct Answer: A
Explanation: Atomic number (29) = protons = electrons in a neutral atom. Mass number
(65) – atomic number = 65 – 29 = 34 neutrons.
2. Which quantum-number set is valid for the last electron added to a neutral
phosphorus atom (Z = 15)?
A. n = 3, l = 2, m = 0, mₛ = +½
B. n = 3, l = 1, m = –1, mₛ = +½
,C. n = 2, l = 1, m = 0, mₛ = –½
D. n = 4, l = 0, m = 0, mₛ = +½
Correct Answer: B
Explanation: Phosphorus ends with 3p³; the third 3p electron enters one of the degenerate
3p orbitals with m = –1, 0, or +1 and parallel spin (Hund’s rule). All values are within
allowed ranges.
3. Arrange the following species in order of increasing first-ionization energy: Mg,
Al, Na, Si.
A. Na < Mg < Al < Si
B. Mg < Na < Al < Si
C. Na < Al < Mg < Si
D. Si < Al < Mg < Na
Correct Answer: A
Explanation: Ionization energy increases left-to-right across a period; Na (period 3, group
1) is lowest, followed by Mg, Al, and Si highest.
4. Which element has the largest atomic radius among S, Cl, Se, and Br?
, A. S
B. Cl
C. Se
D. Br
Correct Answer: D
Explanation: Atomic radius increases down a group and left-to-right across a period. Br is
below Cl in group 17 and below Se in period 4, giving it the largest radius.
5. How many unpaired electrons are present in a ground-state sulfur atom (Z = 16)?
A. 0
B. 1
C. 2
D. 3
Correct Answer: C
Explanation: Sulfur’s configuration is 1s² 2s² 2p⁶ 3s² 3p⁴; the 3p subshell contains two
unpaired electrons (Hund’s rule).
