WGU D425 Introduction to Chemistry Final Proctored
Objective Assessment (OA) Exam | Complete Practice
Questions with Verified Correct Answers & Detailed
Rationales | Latest Update - 2026/2027 Edition
Question 1
What is the product of a synthesis reaction between potassium and
chloride?
A) HCl
B) KBr
C) NaCl
D) KCl
Answer: D
Rationale: A synthesis reaction between potassium (K) and chloride (Cl)
produces potassium chloride (KCl). Potassium has a +1 charge and chloride
has a -1 charge, so they combine in a 1:1 ratio. This is a classic combination
reaction where two elements combine to form a compound.
Question 2
What units are used to measure volume of % concentration?
A) Kilograms
B) Kilometers
C) Milliliters
D) Meters
Answer: C
Rationale: Volume percent concentration (% v/v) uses milliliters (mL) or
liters (L) to measure the volume of solute and solution. Kilograms measure
mass, kilometers and meters measure length/distance. Volume percent is
calculated as (volume of solute / volume of solution) × 100.
Question 3
Talia prepares a bowl of cereal with milk. When she starts to eat the cereal,
she immediately spits it out because the milk has turned sour. Which
pg. 1
,property change is the souring of milk an example of?
A) Chemical change
B) Physical change
C) Nuclear change
D) Condensation
Answer: A
Rationale: Souring of milk is a chemical change because it involves the
formation of new substances (lactic acid) through bacterial fermentation.
Chemical changes produce new substances with different chemical
properties. Physical changes only affect the form or state of matter without
changing the chemical composition.
Question 4
How many valence electrons do alkaline earth metals, like magnesium,
have in their outermost shell?
A) 1 valence electron that is given up in a reaction
B) 2 valence electrons that are given up in a reaction
C) 0 valence electrons that are given up in a reaction
D) 3 valence electrons that are given up in a reaction
Answer: B
Rationale: Alkaline earth metals (Group 2) have 2 valence electrons in
their outermost shell. These electrons are given up in chemical reactions to
form +2 ions (cations). Magnesium (Mg) loses its 2 valence electrons to
achieve a stable octet configuration.
Question 5
How many atoms are in 14 moles of cadmium (Cd)?
A) 8.4 × 10²⁴ atoms Cd
B) 6.02 × 10²³ atoms Cd
C) 1.4 × 10²⁴ atoms Cd
D) 14 atoms Cd
Answer: A
Rationale: To find the number of atoms, multiply the number of moles by
Avogadro's number (6.02 × 10²³ atoms/mol). 14 mol × 6.02 × 10²³
atoms/mol = 8.428 × 10²⁴ atoms Cd ≈ 8.4 × 10²⁴ atoms Cd.
pg. 2
,Question 6
The density of a solution is 0.791 g/cm³. What is the volume in cubic inches
of 2.7 lb of the solution?
A) 2.22 mol
B) 1.5784 g = 1.5 g
C) 95 in³
D) 1.72 g/mL
Answer: C
Rationale: Convert pounds to grams (2.7 lb × 453.592 g/lb = 1224.7 g).
Volume = mass/density = 1224.7 g / 0.791 g/cm³ = 1548.3 cm³. Convert
cm³ to in³ (1 in³ = 16.387 cm³): 1548..387 = 94.5 in³ ≈ 95 in³.
Question 7
What is the definition of the equivalence point in titration?
A) The concentration of each substance in the system will be constant
B) Chemical reactions proceed in both forward and reverse directions at
equal rates
C) The point at which the amount of titrant added is just enough to
completely neutralize the analyte solution
D) The rate for both forward and reverse processes become equal
Answer: C
Rationale: The equivalence point in titration is reached when the amount
of titrant added is stoichiometrically equivalent to the amount of analyte in
the solution. At this point, the reaction between the titrant and analyte is
complete, allowing calculation of the analyte concentration.
Question 8
What mass of hydrogen peroxide must decompose to produce 48.64 g of
water?
2H₂O₂ → O₂ + 2H₂O
A) 91.83 g H₂O₂
B) 48.64 g H₂O₂
C) 34.02 g H₂O₂
D) 18.02 g H₂O₂
pg. 3
, Answer: A
Rationale: Use dimensional analysis: 48.64 g H₂O × (1 mol H₂O / 18.02 g
H₂O) × (2 mol H₂O₂ / 2 mol H₂O) × (34.02 g H₂O₂ / 1 mol H₂O₂) = 91.83
g H₂O₂.
Question 9
What color does a base appear on red litmus paper?
A) Blue
B) Red
C) Yellow
D) Green
Answer: A
Rationale: Bases turn red litmus paper blue. The pigment in red litmus
reacts with OH⁻ ions and changes chemically so the bonds appear blue.
This is a classic acid-base indicator test where red litmus turns blue in basic
solutions and remains red in acidic solutions.
Question 10
What is the correct name for a molecule of SO₃?
A) Sodium trioxide
B) Sulfur trioxide
C) Nitrogen monoxide
D) Silicon dioxide
Answer: B
Rationale: SO₃ is sulfur trioxide. The prefix "tri-" indicates three oxygen
atoms, and sulfur is the first element. The ending "-ide" is used for the
second element with the appropriate prefix. Sodium trioxide would be
Na₂O₃, nitrogen monoxide is NO, and silicon dioxide is SiO₂.
Question 11
Calculate the density in g/mL of aluminum with a volume of 0.6 cm³ and a
mass of 4.6 mg.
A) 0.008 g/mL
B) 0.008 g/cm³
C) 7.67 g/mL
pg. 4
Objective Assessment (OA) Exam | Complete Practice
Questions with Verified Correct Answers & Detailed
Rationales | Latest Update - 2026/2027 Edition
Question 1
What is the product of a synthesis reaction between potassium and
chloride?
A) HCl
B) KBr
C) NaCl
D) KCl
Answer: D
Rationale: A synthesis reaction between potassium (K) and chloride (Cl)
produces potassium chloride (KCl). Potassium has a +1 charge and chloride
has a -1 charge, so they combine in a 1:1 ratio. This is a classic combination
reaction where two elements combine to form a compound.
Question 2
What units are used to measure volume of % concentration?
A) Kilograms
B) Kilometers
C) Milliliters
D) Meters
Answer: C
Rationale: Volume percent concentration (% v/v) uses milliliters (mL) or
liters (L) to measure the volume of solute and solution. Kilograms measure
mass, kilometers and meters measure length/distance. Volume percent is
calculated as (volume of solute / volume of solution) × 100.
Question 3
Talia prepares a bowl of cereal with milk. When she starts to eat the cereal,
she immediately spits it out because the milk has turned sour. Which
pg. 1
,property change is the souring of milk an example of?
A) Chemical change
B) Physical change
C) Nuclear change
D) Condensation
Answer: A
Rationale: Souring of milk is a chemical change because it involves the
formation of new substances (lactic acid) through bacterial fermentation.
Chemical changes produce new substances with different chemical
properties. Physical changes only affect the form or state of matter without
changing the chemical composition.
Question 4
How many valence electrons do alkaline earth metals, like magnesium,
have in their outermost shell?
A) 1 valence electron that is given up in a reaction
B) 2 valence electrons that are given up in a reaction
C) 0 valence electrons that are given up in a reaction
D) 3 valence electrons that are given up in a reaction
Answer: B
Rationale: Alkaline earth metals (Group 2) have 2 valence electrons in
their outermost shell. These electrons are given up in chemical reactions to
form +2 ions (cations). Magnesium (Mg) loses its 2 valence electrons to
achieve a stable octet configuration.
Question 5
How many atoms are in 14 moles of cadmium (Cd)?
A) 8.4 × 10²⁴ atoms Cd
B) 6.02 × 10²³ atoms Cd
C) 1.4 × 10²⁴ atoms Cd
D) 14 atoms Cd
Answer: A
Rationale: To find the number of atoms, multiply the number of moles by
Avogadro's number (6.02 × 10²³ atoms/mol). 14 mol × 6.02 × 10²³
atoms/mol = 8.428 × 10²⁴ atoms Cd ≈ 8.4 × 10²⁴ atoms Cd.
pg. 2
,Question 6
The density of a solution is 0.791 g/cm³. What is the volume in cubic inches
of 2.7 lb of the solution?
A) 2.22 mol
B) 1.5784 g = 1.5 g
C) 95 in³
D) 1.72 g/mL
Answer: C
Rationale: Convert pounds to grams (2.7 lb × 453.592 g/lb = 1224.7 g).
Volume = mass/density = 1224.7 g / 0.791 g/cm³ = 1548.3 cm³. Convert
cm³ to in³ (1 in³ = 16.387 cm³): 1548..387 = 94.5 in³ ≈ 95 in³.
Question 7
What is the definition of the equivalence point in titration?
A) The concentration of each substance in the system will be constant
B) Chemical reactions proceed in both forward and reverse directions at
equal rates
C) The point at which the amount of titrant added is just enough to
completely neutralize the analyte solution
D) The rate for both forward and reverse processes become equal
Answer: C
Rationale: The equivalence point in titration is reached when the amount
of titrant added is stoichiometrically equivalent to the amount of analyte in
the solution. At this point, the reaction between the titrant and analyte is
complete, allowing calculation of the analyte concentration.
Question 8
What mass of hydrogen peroxide must decompose to produce 48.64 g of
water?
2H₂O₂ → O₂ + 2H₂O
A) 91.83 g H₂O₂
B) 48.64 g H₂O₂
C) 34.02 g H₂O₂
D) 18.02 g H₂O₂
pg. 3
, Answer: A
Rationale: Use dimensional analysis: 48.64 g H₂O × (1 mol H₂O / 18.02 g
H₂O) × (2 mol H₂O₂ / 2 mol H₂O) × (34.02 g H₂O₂ / 1 mol H₂O₂) = 91.83
g H₂O₂.
Question 9
What color does a base appear on red litmus paper?
A) Blue
B) Red
C) Yellow
D) Green
Answer: A
Rationale: Bases turn red litmus paper blue. The pigment in red litmus
reacts with OH⁻ ions and changes chemically so the bonds appear blue.
This is a classic acid-base indicator test where red litmus turns blue in basic
solutions and remains red in acidic solutions.
Question 10
What is the correct name for a molecule of SO₃?
A) Sodium trioxide
B) Sulfur trioxide
C) Nitrogen monoxide
D) Silicon dioxide
Answer: B
Rationale: SO₃ is sulfur trioxide. The prefix "tri-" indicates three oxygen
atoms, and sulfur is the first element. The ending "-ide" is used for the
second element with the appropriate prefix. Sodium trioxide would be
Na₂O₃, nitrogen monoxide is NO, and silicon dioxide is SiO₂.
Question 11
Calculate the density in g/mL of aluminum with a volume of 0.6 cm³ and a
mass of 4.6 mg.
A) 0.008 g/mL
B) 0.008 g/cm³
C) 7.67 g/mL
pg. 4
