WGU D425 INTRO TO CHEMISTRY
OBJECTIVE ASSESSMENT PREP
QUESTIONS WITH VERIFIED ANSWERS
2026/2027.
1. An isotope of an element has a mass number of 75 and 42 neutrons. Which of the following
is the correct symbol and number of electrons for a neutral atom of this isotope?
A. As, 42 electrons
B. Mo, 42 electrons
C. Re, 75 electrons
D. As, 33 electrons
Answer: D
Conceptual Explanation: The atomic number (number of protons) is calculated by
subtracting neutrons from the mass number: 75 - 42 = 33. Element 33 is Arsenic (As). In a
neutral atom, electrons equal protons.
,2. Which of the following electronic transitions in a hydrogen atom would result in the
emission of the highest energy photon?
A. n=2 to n=1
B. n=5 to n=2
C. n=1 to n=4
D. n=4 to n=3
Answer: A
Conceptual Explanation: Emission occurs when an electron drops to a lower energy level.
The transition from n=2 to n=1 involves the largest energy gap in the hydrogen atom series
compared to transitions between higher levels.
3. Which molecule possesses a central atom with sp3d2 hybridization and a square planar
molecular geometry?
A. SF6
B. BrF5
C. PF5
D. XeF4
Answer: D
, Conceptual Explanation: XeF4 has 6 electron domains (4 bonding, 2 lone pairs) around
Xenon, resulting in sp3d2 hybridization and a square planar geometry to minimize
repulsion.
4. Given the reaction: 2 Al + 3 Cl2 -> 2 AlCl3. If 5.0 moles of Al react with 6.0 moles of Cl2,
what is the limiting reactant and how many moles of AlCl3 are produced?
A. Al is limiting; 5.0 moles AlCl3
B. Cl2 is limiting; 4.0 moles AlCl3
C. Al is limiting; 2.5 moles AlCl3
D. Cl2 is limiting; 6.0 moles AlCl3
Answer: B
Conceptual Explanation: The molar ratio is 2:3. 5 moles Al needs 7.5 moles Cl2. Since only
6 moles Cl2 are available, Cl2 is limiting. (6 mol Cl2) * (2 mol AlCl mol Cl2) = 4 mol
AlCl3.
5. What is the formal charge on the central nitrogen atom in the azide ion (N3-)?
A. -1
B. 0
C. +2
D. +1
Answer: D
OBJECTIVE ASSESSMENT PREP
QUESTIONS WITH VERIFIED ANSWERS
2026/2027.
1. An isotope of an element has a mass number of 75 and 42 neutrons. Which of the following
is the correct symbol and number of electrons for a neutral atom of this isotope?
A. As, 42 electrons
B. Mo, 42 electrons
C. Re, 75 electrons
D. As, 33 electrons
Answer: D
Conceptual Explanation: The atomic number (number of protons) is calculated by
subtracting neutrons from the mass number: 75 - 42 = 33. Element 33 is Arsenic (As). In a
neutral atom, electrons equal protons.
,2. Which of the following electronic transitions in a hydrogen atom would result in the
emission of the highest energy photon?
A. n=2 to n=1
B. n=5 to n=2
C. n=1 to n=4
D. n=4 to n=3
Answer: A
Conceptual Explanation: Emission occurs when an electron drops to a lower energy level.
The transition from n=2 to n=1 involves the largest energy gap in the hydrogen atom series
compared to transitions between higher levels.
3. Which molecule possesses a central atom with sp3d2 hybridization and a square planar
molecular geometry?
A. SF6
B. BrF5
C. PF5
D. XeF4
Answer: D
, Conceptual Explanation: XeF4 has 6 electron domains (4 bonding, 2 lone pairs) around
Xenon, resulting in sp3d2 hybridization and a square planar geometry to minimize
repulsion.
4. Given the reaction: 2 Al + 3 Cl2 -> 2 AlCl3. If 5.0 moles of Al react with 6.0 moles of Cl2,
what is the limiting reactant and how many moles of AlCl3 are produced?
A. Al is limiting; 5.0 moles AlCl3
B. Cl2 is limiting; 4.0 moles AlCl3
C. Al is limiting; 2.5 moles AlCl3
D. Cl2 is limiting; 6.0 moles AlCl3
Answer: B
Conceptual Explanation: The molar ratio is 2:3. 5 moles Al needs 7.5 moles Cl2. Since only
6 moles Cl2 are available, Cl2 is limiting. (6 mol Cl2) * (2 mol AlCl mol Cl2) = 4 mol
AlCl3.
5. What is the formal charge on the central nitrogen atom in the azide ion (N3-)?
A. -1
B. 0
C. +2
D. +1
Answer: D
