,CHEM 103 Module 4 | Actual Questions and Answers + Rationales | 2026/27
Updates | 100% correct
1. Which topic is typically covered in Module 4 of a general chemistry course?
A) Stoichiometry
B) Molecular geometry and polarity
C) Nuclear chemistry
D) Chemical kinetics
Correct Answer: Molecular geometry and polarity
Rationale: Based on the course content descriptions for CHEM 103, Module 4 typically covers
electron configurations, periodic trends, chemical bonding, Lewis structures, and molecular
geometry . Molecular geometry, including VSEPR theory and bond polarity, is a central topic in
this module.
2. What is the correct electron configuration for phosphorus (P, Z=15)?
A) 1s² 2s² 2p⁶ 3s² 3p³
B) 1s² 2s² 2p⁶ 3s² 3p⁴
C) 1s² 2s² 2p⁶ 3s² 3p²
D) 1s² 2s² 2p⁶ 3s¹ 3p⁴
Correct Answer: 1s² 2s² 2p⁶ 3s² 3p³
Rationale: Phosphorus has 15 electrons. Following the Aufbau principle, the configuration is
filled in order of increasing energy levels: 1s² (2), 2s² (4), 2p⁶ (10), 3s² (12), and finally 3p³ (15).
This is the ground-state configuration.
,3. According to the Pauli Exclusion Principle, what is true about two electrons in the same
orbital?
A) They must have the same spin
B) They must have opposite spins
C) They must have identical quantum numbers
D) They cannot occupy the same orbital
Correct Answer: They must have opposite spins
Rationale: The Pauli Exclusion Principle states that no two electrons in an atom can have the
same set of four quantum numbers . Therefore, if two electrons share the same orbital (same n,
l, and ml), they must differ in their spin quantum number (ms), which means one has spin +1/2
and the other has spin -1/2.
4. What is the correct order of orbital filling according to the Aufbau Principle?
A) 1s, 2s, 2p, 3s, 3p, 3d, 4s
B) 1s, 2s, 2p, 3s, 3p, 4s, 3d
C) 1s, 2s, 3s, 2p, 3p, 4s, 3d
D) 1s, 2s, 2p, 3s, 4s, 3p, 3d
Correct Answer: 1s, 2s, 2p, 3s, 3p, 4s, 3d
Rationale: The Aufbau Principle states that electrons occupy the lowest available energy levels
first . The standard order of filling is: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, etc. Note that 4s is lower in
energy than 3d and is filled first.
5. Which rule states that electrons will fill orbitals of the same energy singly before pairing up?
A) Aufbau Principle
, B) Pauli Exclusion Principle
C) Hund's Rule
D) Heisenberg Uncertainty Principle
Correct Answer: Hund's Rule
Rationale: Hund's Rule states that due to electron-electron repulsion, electrons will occupy
orbitals of the same energy (degenerate orbitals) singly as much as possible before any pairing
occurs . This maximizes the number of unpaired electrons and results in the lowest energy
configuration.
6. Which of the following elements has the electron configuration [Ne]3s²3p³?
A) Nitrogen
B) Phosphorus
C) Arsenic
D) Sulfur
Correct Answer: Phosphorus
Rationale: [Ne] represents the electron configuration of neon (1s²2s²2p⁶). Adding 3s²3p³ gives a
total of 15 electrons, which is the atomic number of phosphorus.
7. What is the maximum number of electrons that can occupy the 3d subshell?
A) 2
B) 6
C) 10
D) 14
Updates | 100% correct
1. Which topic is typically covered in Module 4 of a general chemistry course?
A) Stoichiometry
B) Molecular geometry and polarity
C) Nuclear chemistry
D) Chemical kinetics
Correct Answer: Molecular geometry and polarity
Rationale: Based on the course content descriptions for CHEM 103, Module 4 typically covers
electron configurations, periodic trends, chemical bonding, Lewis structures, and molecular
geometry . Molecular geometry, including VSEPR theory and bond polarity, is a central topic in
this module.
2. What is the correct electron configuration for phosphorus (P, Z=15)?
A) 1s² 2s² 2p⁶ 3s² 3p³
B) 1s² 2s² 2p⁶ 3s² 3p⁴
C) 1s² 2s² 2p⁶ 3s² 3p²
D) 1s² 2s² 2p⁶ 3s¹ 3p⁴
Correct Answer: 1s² 2s² 2p⁶ 3s² 3p³
Rationale: Phosphorus has 15 electrons. Following the Aufbau principle, the configuration is
filled in order of increasing energy levels: 1s² (2), 2s² (4), 2p⁶ (10), 3s² (12), and finally 3p³ (15).
This is the ground-state configuration.
,3. According to the Pauli Exclusion Principle, what is true about two electrons in the same
orbital?
A) They must have the same spin
B) They must have opposite spins
C) They must have identical quantum numbers
D) They cannot occupy the same orbital
Correct Answer: They must have opposite spins
Rationale: The Pauli Exclusion Principle states that no two electrons in an atom can have the
same set of four quantum numbers . Therefore, if two electrons share the same orbital (same n,
l, and ml), they must differ in their spin quantum number (ms), which means one has spin +1/2
and the other has spin -1/2.
4. What is the correct order of orbital filling according to the Aufbau Principle?
A) 1s, 2s, 2p, 3s, 3p, 3d, 4s
B) 1s, 2s, 2p, 3s, 3p, 4s, 3d
C) 1s, 2s, 3s, 2p, 3p, 4s, 3d
D) 1s, 2s, 2p, 3s, 4s, 3p, 3d
Correct Answer: 1s, 2s, 2p, 3s, 3p, 4s, 3d
Rationale: The Aufbau Principle states that electrons occupy the lowest available energy levels
first . The standard order of filling is: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, etc. Note that 4s is lower in
energy than 3d and is filled first.
5. Which rule states that electrons will fill orbitals of the same energy singly before pairing up?
A) Aufbau Principle
, B) Pauli Exclusion Principle
C) Hund's Rule
D) Heisenberg Uncertainty Principle
Correct Answer: Hund's Rule
Rationale: Hund's Rule states that due to electron-electron repulsion, electrons will occupy
orbitals of the same energy (degenerate orbitals) singly as much as possible before any pairing
occurs . This maximizes the number of unpaired electrons and results in the lowest energy
configuration.
6. Which of the following elements has the electron configuration [Ne]3s²3p³?
A) Nitrogen
B) Phosphorus
C) Arsenic
D) Sulfur
Correct Answer: Phosphorus
Rationale: [Ne] represents the electron configuration of neon (1s²2s²2p⁶). Adding 3s²3p³ gives a
total of 15 electrons, which is the atomic number of phosphorus.
7. What is the maximum number of electrons that can occupy the 3d subshell?
A) 2
B) 6
C) 10
D) 14
