WGU D425 Study Guide | Latest Update 2026/2027
200 Questions and Verified Answers | Actual Assessment Q&A |
100% Correct
SECTION 1: ATOMIC STRUCTURE & PERIODIC TRENDS (Questions 1–40)
1. What is the atomic number of an element?
A) The number of neutrons in the nucleus
B) The number of protons in the nucleus
C) The total number of protons and neutrons
D) The number of electrons in the outermost shell
Correct Answer: B
Rationale: The atomic number (Z) equals the number of protons in the nucleus of an atom. This number
defines the element and determines its identity on the periodic table. For a neutral atom, the number of
protons equals the number of electrons.
2. An atom has 6 protons, 6 neutrons, and 6 electrons. What is its mass number?
A) 6
B) 12
C) 18
D) 24
Correct Answer: B
,Rationale: The mass number is the total number of protons and neutrons in the nucleus. Mass number =
protons + neutrons = 6 + 6 = 12. This atom is carbon12, the most common isotope of carbon.
3. Isotopes of the same element differ in the number of:
A) Protons
B) Neutrons
C) Electrons
D) Positrons
Correct Answer: B
Rationale: Isotopes are atoms of the same element that have the same number of protons but different
numbers of neutrons. This results in different mass numbers while maintaining the same atomic number
and chemical properties.
4. Which subatomic particle has a negative charge?
A) Proton
B) Neutron
C) Electron
D) Positron
Correct Answer: C
Rationale: Electrons are negatively charged subatomic particles that orbit the nucleus in electron shells.
Protons are positively charged, and neutrons have no charge. Positrons are antimatter particles with a
positive charge.
,5. Where is the majority of the atomic mass concentrated in an atom?
A) Orbitals
B) Nucleus
C) Shells
D) Subshells
Correct Answer: B
Rationale: The nucleus contains protons and neutrons, which account for nearly all of the atomic mass.
Electrons have negligible mass compared to protons and neutrons. The nucleus is extremely dense and
contains more than 99.9% of the atom's mass.
6. What is the correct electron configuration for carbon (atomic number 6)?
A) 1s² 2s² 2p²
B) 1s² 2s² 2p⁶
C) 1s² 2s¹ 2p³
D) 1s² 2s² 2p⁴
Correct Answer: A
Rationale: Carbon has 6 electrons: 1s² (2 electrons), 2s² (2 electrons), and 2p² (2 electrons) = total 6
electrons. The electron configuration follows the Aufbau principle, filling lower energy orbitals first.
, 7. Which element has the electron configuration 1s² 2s² 2p⁶ 3s¹?
A) Sodium (Na)
B) Magnesium (Mg)
C) Neon (Ne)
D) Lithium (Li)
Correct Answer: A
Rationale: 1s² 2s² 2p⁶ accounts for 10 electrons (Neon configuration), plus 3s¹ adds 1 electron for a total
of 11 electrons. The element with atomic number 11 is sodium (Na). This electron configuration
represents sodium's ground state.
8. How many valence electrons does oxygen (atomic number 8) have?
A) 2
B) 4
C) 6
D) 8
Correct Answer: C
Rationale: Oxygen has the electron configuration 1s² 2s² 2p⁴. The valence electrons are those in the
outermost shell (n=2): 2s² + 2p⁴ = 6 valence electrons. Oxygen needs 2 more electrons to achieve a
stable octet.
9. What is the trend for atomic radius on the periodic table?
200 Questions and Verified Answers | Actual Assessment Q&A |
100% Correct
SECTION 1: ATOMIC STRUCTURE & PERIODIC TRENDS (Questions 1–40)
1. What is the atomic number of an element?
A) The number of neutrons in the nucleus
B) The number of protons in the nucleus
C) The total number of protons and neutrons
D) The number of electrons in the outermost shell
Correct Answer: B
Rationale: The atomic number (Z) equals the number of protons in the nucleus of an atom. This number
defines the element and determines its identity on the periodic table. For a neutral atom, the number of
protons equals the number of electrons.
2. An atom has 6 protons, 6 neutrons, and 6 electrons. What is its mass number?
A) 6
B) 12
C) 18
D) 24
Correct Answer: B
,Rationale: The mass number is the total number of protons and neutrons in the nucleus. Mass number =
protons + neutrons = 6 + 6 = 12. This atom is carbon12, the most common isotope of carbon.
3. Isotopes of the same element differ in the number of:
A) Protons
B) Neutrons
C) Electrons
D) Positrons
Correct Answer: B
Rationale: Isotopes are atoms of the same element that have the same number of protons but different
numbers of neutrons. This results in different mass numbers while maintaining the same atomic number
and chemical properties.
4. Which subatomic particle has a negative charge?
A) Proton
B) Neutron
C) Electron
D) Positron
Correct Answer: C
Rationale: Electrons are negatively charged subatomic particles that orbit the nucleus in electron shells.
Protons are positively charged, and neutrons have no charge. Positrons are antimatter particles with a
positive charge.
,5. Where is the majority of the atomic mass concentrated in an atom?
A) Orbitals
B) Nucleus
C) Shells
D) Subshells
Correct Answer: B
Rationale: The nucleus contains protons and neutrons, which account for nearly all of the atomic mass.
Electrons have negligible mass compared to protons and neutrons. The nucleus is extremely dense and
contains more than 99.9% of the atom's mass.
6. What is the correct electron configuration for carbon (atomic number 6)?
A) 1s² 2s² 2p²
B) 1s² 2s² 2p⁶
C) 1s² 2s¹ 2p³
D) 1s² 2s² 2p⁴
Correct Answer: A
Rationale: Carbon has 6 electrons: 1s² (2 electrons), 2s² (2 electrons), and 2p² (2 electrons) = total 6
electrons. The electron configuration follows the Aufbau principle, filling lower energy orbitals first.
, 7. Which element has the electron configuration 1s² 2s² 2p⁶ 3s¹?
A) Sodium (Na)
B) Magnesium (Mg)
C) Neon (Ne)
D) Lithium (Li)
Correct Answer: A
Rationale: 1s² 2s² 2p⁶ accounts for 10 electrons (Neon configuration), plus 3s¹ adds 1 electron for a total
of 11 electrons. The element with atomic number 11 is sodium (Na). This electron configuration
represents sodium's ground state.
8. How many valence electrons does oxygen (atomic number 8) have?
A) 2
B) 4
C) 6
D) 8
Correct Answer: C
Rationale: Oxygen has the electron configuration 1s² 2s² 2p⁴. The valence electrons are those in the
outermost shell (n=2): 2s² + 2p⁴ = 6 valence electrons. Oxygen needs 2 more electrons to achieve a
stable octet.
9. What is the trend for atomic radius on the periodic table?
