WGU D425 INTRO TO CHEMISTRY
OBJECTIVE ASSESSMENT EXAM BANK
150 EXPERT Q and AS WITH
COMPREHENSIVE RATIONALES 2025
2026 ULTIMATE STUDY PACK
WGU D425 Intro to Chemistry Objective Assessment
Master Bank (Questions 1–150)
1. A student is investigating the subatomic particles of
a neutral atom of Sulfur-32 (\(^{32}_{16}\text{S}\)).
Which of the following statements correctly identifies
the composition and location of the subatomic
particles within this atom?
A) 16 protons and 16 electrons are located inside the nucleus,
while 32 neutrons orbit in the electron cloud.
B) Correct Answer: 16 protons and 16 neutrons are
tightly packed inside the central nucleus, while 16
electrons reside in the surrounding electron cloud.
C) 32 protons are located in the nucleus, while 16 neutrons and
16 electrons are distributed uniformly throughout the atom.
D) 16 neutrons and 16 electrons reside in the nucleus, while 32
protons orbit in discrete energy shells.
Rationale: The atomic number of Sulfur is 16, which defines its
number of protons. In a neutral atom, the number of electrons
equals the number of protons (16). The mass number is 32,
meaning the number of neutrons is calculated as mass number
minus atomic number (\(32 - 16 = 16\)). Protons and neutrons
reside exclusively in the nucleus, whereas electrons occupy the
electron cloud.
2. An experiment requires identifying an element that
exhibits high electrical conductivity, malleability, a
,shiny luster, and readily loses electrons to form
cations. In which region of the periodic table is this
element most likely located?
A) On the far upper right side among the nonmetals.
B) Along the diagonal zig-zag staircase line containing the
metalloids.
C) Correct Answer: On the left side and center of the
periodic table among the metals.
D) Exclusively in Group 18 within the unreactive noble gases.
Rationale: The described physical and chemical properties
(conductivity, malleability, luster, and tendency to form
positive ions/cations by losing valence electrons) are classic
characteristics of metals. Metals make up the vast majority of
elements and are situated on the left side and across the
central d-block of the periodic table.
3. When moving from left to right across Period 3 of
the periodic table (from Sodium to Argon), what is the
general trend observed regarding atomic radius, and
what electrostatic phenomenon drives this change?
A) Atomic radius increases because the addition of new
principal energy levels pushes electrons further outward.
B) Atomic radius remains completely constant because the
number of core shielding electrons increases at the same rate.
C) Correct Answer: Atomic radius decreases because
the increasing nuclear charge draws the valence
electrons closer to the nucleus.
D) Atomic radius decreases because the electrons repel each
other progressively, causing the cloud to shrink.
Rationale: As you move from left to right across a single
period, protons are steadily added to the nucleus, increasing
the positive nuclear charge (\(Z_{\text{eff}}\)). Because the
additional electrons are being added to the same principal
energy shell, the core electron shielding remains constant. The
stronger nuclear pull draws the valence electron cloud inward,
shrinking the atomic radius.
,4. A sample of an unknown compound is analyzed in a
laboratory. The substance has a high melting point, is
brittle, dissolves easily in water, and conducts
electricity efficiently when dissolved in an aqueous
solution, but not in its solid state. What type of
chemical bonding is present in this compound?
A) Covalent bonding formed by the equal sharing of valence
electrons between two nonmetals.
B) Metallic bonding characterized by a localized sea of
delocalized mobile electrons.
C) Correct Answer: Ionic bonding formed by the
electrostatic attraction between a metal cation and a
nonmetal anion.
D) Network covalent bonding held together by weak
intermolecular van der Waals forces.
Rationale: Ionic compounds consist of structured crystalline
lattices held together by strong electrostatic attractions
between oppositely charged ions. They require high energy to
melt, cleave along straight lines when struck (brittle), and
dissociate into free-moving mobile ions when dissolved in
water, allowing them to conduct electricity (electrolytes).
5. Consider the balanced chemical equation
representing the combustion of propane:
\(\text{C}_3\text{H}_8 + 5\text{O}_2 \rightarrow
3\text{CO}_2 + 4\text{H}_2\text{O}\). If a chemist
reacts 2.0 moles of propane
(\(\text{C}_3\text{H}_8\)) with an excess of oxygen
gas, how many moles of water
(\(\text{H}_2\text{O}\)) will be theoretically
produced?
A) 2.0 moles
B) 4.0 moles
C) Correct Answer: 8.0 moles
D) 10.0 moles
Rationale: The balanced equation establishes a stoichiometric
, molar ratio between propane (\(\text{C}_3\text{H}_8\)) and
water (\(\text{H}_2\text{O}\)) of 1:4. Using dimensional
analysis: \(2.0\text{ moles C}_3\text{H}_8 \times (4\text{
moles H}_2\text{O} / 1\text{ mole C}_3\text{H}_8) =
8.0\text{ moles H}_2\text{O}\).
6. A container holds a sample of an ideal gas at a
constant temperature. If the volume of the container is
compressed to exactly half of its original size, what
will be the resulting effect on the pressure of the gas,
according to Boyle's Law?
A) The pressure will drop to one-half of its original value
because particles hit the walls less frequently.
B) The pressure will remain completely unchanged because
temperature dictates molecular speed.
C) Correct Answer: The pressure will double because
gas particles are confined to a smaller space and
collide with the walls twice as frequently.
D) The pressure will quadruple due to exponential increases in
intermolecular kinetic energy.
Rationale: Boyle's Law states that at a constant temperature,
the pressure and volume of a gas have an inversely
proportional relationship (\(P_1V_1 = P_2V_2\)). If the
volume is halved (\(1/2\ V\)), the pressure must change by the
inverse factor, which means it doubles (\(2\times P\)), because
compressing the volume forces the gas molecules into less
space, doubling the frequency of wall collisions.
7. Which of the following statements accurately
summarizes the fundamental behavior of matter in the
solid state compared to the liquid and gas states, based
on the Kinetic Molecular Theory?
A) Solid particles possess high kinetic energy and completely
overcome intermolecular forces to fill the container volume.
B) Solid particles flow freely past one another and assume the
precise shape of whatever container they occupy.
OBJECTIVE ASSESSMENT EXAM BANK
150 EXPERT Q and AS WITH
COMPREHENSIVE RATIONALES 2025
2026 ULTIMATE STUDY PACK
WGU D425 Intro to Chemistry Objective Assessment
Master Bank (Questions 1–150)
1. A student is investigating the subatomic particles of
a neutral atom of Sulfur-32 (\(^{32}_{16}\text{S}\)).
Which of the following statements correctly identifies
the composition and location of the subatomic
particles within this atom?
A) 16 protons and 16 electrons are located inside the nucleus,
while 32 neutrons orbit in the electron cloud.
B) Correct Answer: 16 protons and 16 neutrons are
tightly packed inside the central nucleus, while 16
electrons reside in the surrounding electron cloud.
C) 32 protons are located in the nucleus, while 16 neutrons and
16 electrons are distributed uniformly throughout the atom.
D) 16 neutrons and 16 electrons reside in the nucleus, while 32
protons orbit in discrete energy shells.
Rationale: The atomic number of Sulfur is 16, which defines its
number of protons. In a neutral atom, the number of electrons
equals the number of protons (16). The mass number is 32,
meaning the number of neutrons is calculated as mass number
minus atomic number (\(32 - 16 = 16\)). Protons and neutrons
reside exclusively in the nucleus, whereas electrons occupy the
electron cloud.
2. An experiment requires identifying an element that
exhibits high electrical conductivity, malleability, a
,shiny luster, and readily loses electrons to form
cations. In which region of the periodic table is this
element most likely located?
A) On the far upper right side among the nonmetals.
B) Along the diagonal zig-zag staircase line containing the
metalloids.
C) Correct Answer: On the left side and center of the
periodic table among the metals.
D) Exclusively in Group 18 within the unreactive noble gases.
Rationale: The described physical and chemical properties
(conductivity, malleability, luster, and tendency to form
positive ions/cations by losing valence electrons) are classic
characteristics of metals. Metals make up the vast majority of
elements and are situated on the left side and across the
central d-block of the periodic table.
3. When moving from left to right across Period 3 of
the periodic table (from Sodium to Argon), what is the
general trend observed regarding atomic radius, and
what electrostatic phenomenon drives this change?
A) Atomic radius increases because the addition of new
principal energy levels pushes electrons further outward.
B) Atomic radius remains completely constant because the
number of core shielding electrons increases at the same rate.
C) Correct Answer: Atomic radius decreases because
the increasing nuclear charge draws the valence
electrons closer to the nucleus.
D) Atomic radius decreases because the electrons repel each
other progressively, causing the cloud to shrink.
Rationale: As you move from left to right across a single
period, protons are steadily added to the nucleus, increasing
the positive nuclear charge (\(Z_{\text{eff}}\)). Because the
additional electrons are being added to the same principal
energy shell, the core electron shielding remains constant. The
stronger nuclear pull draws the valence electron cloud inward,
shrinking the atomic radius.
,4. A sample of an unknown compound is analyzed in a
laboratory. The substance has a high melting point, is
brittle, dissolves easily in water, and conducts
electricity efficiently when dissolved in an aqueous
solution, but not in its solid state. What type of
chemical bonding is present in this compound?
A) Covalent bonding formed by the equal sharing of valence
electrons between two nonmetals.
B) Metallic bonding characterized by a localized sea of
delocalized mobile electrons.
C) Correct Answer: Ionic bonding formed by the
electrostatic attraction between a metal cation and a
nonmetal anion.
D) Network covalent bonding held together by weak
intermolecular van der Waals forces.
Rationale: Ionic compounds consist of structured crystalline
lattices held together by strong electrostatic attractions
between oppositely charged ions. They require high energy to
melt, cleave along straight lines when struck (brittle), and
dissociate into free-moving mobile ions when dissolved in
water, allowing them to conduct electricity (electrolytes).
5. Consider the balanced chemical equation
representing the combustion of propane:
\(\text{C}_3\text{H}_8 + 5\text{O}_2 \rightarrow
3\text{CO}_2 + 4\text{H}_2\text{O}\). If a chemist
reacts 2.0 moles of propane
(\(\text{C}_3\text{H}_8\)) with an excess of oxygen
gas, how many moles of water
(\(\text{H}_2\text{O}\)) will be theoretically
produced?
A) 2.0 moles
B) 4.0 moles
C) Correct Answer: 8.0 moles
D) 10.0 moles
Rationale: The balanced equation establishes a stoichiometric
, molar ratio between propane (\(\text{C}_3\text{H}_8\)) and
water (\(\text{H}_2\text{O}\)) of 1:4. Using dimensional
analysis: \(2.0\text{ moles C}_3\text{H}_8 \times (4\text{
moles H}_2\text{O} / 1\text{ mole C}_3\text{H}_8) =
8.0\text{ moles H}_2\text{O}\).
6. A container holds a sample of an ideal gas at a
constant temperature. If the volume of the container is
compressed to exactly half of its original size, what
will be the resulting effect on the pressure of the gas,
according to Boyle's Law?
A) The pressure will drop to one-half of its original value
because particles hit the walls less frequently.
B) The pressure will remain completely unchanged because
temperature dictates molecular speed.
C) Correct Answer: The pressure will double because
gas particles are confined to a smaller space and
collide with the walls twice as frequently.
D) The pressure will quadruple due to exponential increases in
intermolecular kinetic energy.
Rationale: Boyle's Law states that at a constant temperature,
the pressure and volume of a gas have an inversely
proportional relationship (\(P_1V_1 = P_2V_2\)). If the
volume is halved (\(1/2\ V\)), the pressure must change by the
inverse factor, which means it doubles (\(2\times P\)), because
compressing the volume forces the gas molecules into less
space, doubling the frequency of wall collisions.
7. Which of the following statements accurately
summarizes the fundamental behavior of matter in the
solid state compared to the liquid and gas states, based
on the Kinetic Molecular Theory?
A) Solid particles possess high kinetic energy and completely
overcome intermolecular forces to fill the container volume.
B) Solid particles flow freely past one another and assume the
precise shape of whatever container they occupy.
