WGU D425 INTRO TO CHEMISTRY
ADVANCED OBJECTIVE ASSESSMENT
QUESTIONS WITH VERIFIED ANSWERS
2026/2027.
1. Which set of quantum numbers (n, l, ml, ms) represents the highest energy electron in a
ground-state Gallium (Ga) atom?
A. 3, 2, 2, +1/2
B. 4, 0, 0, -1/2
C. 4, 1, -1, +1/2
D. 4, 1, 2, +1/2
Answer: C
Conceptual Explanation: Gallium’s valence electron configuration is [Ar] 4s2 3d10 4p1.
The highest energy electron is in the 4p orbital, where n=4 and l=1. The ml value can be -1,
0, or 1, and ms can be +/- 1/2. Option D is invalid because ml cannot exceed l.
2. Calculate the mass of magnesium oxide (MgO) produced when 2.43 g of Mg reacts with
excess oxygen, given a 75% yield.
A. 3.02 g
B. 4.03 g
,C. 2.01 g
D. 6.05 g
Answer: A
Conceptual Explanation: 2.43g Mg / 24.31g/mol = 0.1 mol. Mg + 1/2 O2 -> MgO.
Theoretical yield is 0.1 mol MgO * 40.3g/mol = 4.03g. Actual yield = 4.03g * 0.75 = 3.02g.
3. Which of the following molecules possesses a permanent dipole moment?
A. BrF5
B. PCl5
C. SF6
D. CO2
Answer: A
Conceptual Explanation: BrF5 has a square pyramidal geometry (AX5E) which is
asymmetrical, leading to a net dipole moment. The others are highly symmetrical
(octahedral, trigonal bipyramidal, linear) and their bond dipoles cancel.
4. For the reaction 2A + B -> C, the rate law is rate = k[A]^2. If the volume of the container is
halved, what happens to the reaction rate?
A. Increases by a factor of 4
B. Increases by a factor of 2
C. Increases by a factor of 8
, D. Decreases by a factor of 4
Answer: A
Conceptual Explanation: Halving the volume doubles the concentration of A. Since the
rate depends on [A]^2, the new rate is k(2[A])^2 = 4k[A]^2, a 4-fold increase.
5. A 5.00 L flask contains 0.50 mol of N2 and 0.80 mol of He at 27 degrees Celsius. What is the
partial pressure of N2?
A. 2.46 atm
B. 1.23 atm
C. 3.94 atm
D. 6.40 atm
Answer: B
Conceptual Explanation: P(N2) = n(N2)RT/V = (0.50 mol * 0.0821 Latm/molK * 300K) /
5.00 L = 1.2315 atm.
6. Which element has the highest second ionization energy?
A. Aluminum (Al)
B. Magnesium (Mg)
C. Sodium (Na)
D. Calcium (Ca)
ADVANCED OBJECTIVE ASSESSMENT
QUESTIONS WITH VERIFIED ANSWERS
2026/2027.
1. Which set of quantum numbers (n, l, ml, ms) represents the highest energy electron in a
ground-state Gallium (Ga) atom?
A. 3, 2, 2, +1/2
B. 4, 0, 0, -1/2
C. 4, 1, -1, +1/2
D. 4, 1, 2, +1/2
Answer: C
Conceptual Explanation: Gallium’s valence electron configuration is [Ar] 4s2 3d10 4p1.
The highest energy electron is in the 4p orbital, where n=4 and l=1. The ml value can be -1,
0, or 1, and ms can be +/- 1/2. Option D is invalid because ml cannot exceed l.
2. Calculate the mass of magnesium oxide (MgO) produced when 2.43 g of Mg reacts with
excess oxygen, given a 75% yield.
A. 3.02 g
B. 4.03 g
,C. 2.01 g
D. 6.05 g
Answer: A
Conceptual Explanation: 2.43g Mg / 24.31g/mol = 0.1 mol. Mg + 1/2 O2 -> MgO.
Theoretical yield is 0.1 mol MgO * 40.3g/mol = 4.03g. Actual yield = 4.03g * 0.75 = 3.02g.
3. Which of the following molecules possesses a permanent dipole moment?
A. BrF5
B. PCl5
C. SF6
D. CO2
Answer: A
Conceptual Explanation: BrF5 has a square pyramidal geometry (AX5E) which is
asymmetrical, leading to a net dipole moment. The others are highly symmetrical
(octahedral, trigonal bipyramidal, linear) and their bond dipoles cancel.
4. For the reaction 2A + B -> C, the rate law is rate = k[A]^2. If the volume of the container is
halved, what happens to the reaction rate?
A. Increases by a factor of 4
B. Increases by a factor of 2
C. Increases by a factor of 8
, D. Decreases by a factor of 4
Answer: A
Conceptual Explanation: Halving the volume doubles the concentration of A. Since the
rate depends on [A]^2, the new rate is k(2[A])^2 = 4k[A]^2, a 4-fold increase.
5. A 5.00 L flask contains 0.50 mol of N2 and 0.80 mol of He at 27 degrees Celsius. What is the
partial pressure of N2?
A. 2.46 atm
B. 1.23 atm
C. 3.94 atm
D. 6.40 atm
Answer: B
Conceptual Explanation: P(N2) = n(N2)RT/V = (0.50 mol * 0.0821 Latm/molK * 300K) /
5.00 L = 1.2315 atm.
6. Which element has the highest second ionization energy?
A. Aluminum (Al)
B. Magnesium (Mg)
C. Sodium (Na)
D. Calcium (Ca)
