WGU D425 Intro to Chemistry
Objective Assessment Actual Exam
2025/2026 | Questions with
Verified Answers with Rationale |
Guaranteed Pass |Graded A+
Elements, Compounds, and Mixtures
1. Which of the following is a compound?
A) Air
B) Sodium
C) Water
D) Gold
Answer: C) Water
Rationale: Water (H₂O) is a substance with a fixed composition of
two elements chemically bonded. Air is a mixture, and sodium
(Na) and gold (Au) are elements.
2. A homogeneous mixture is best described as having:
A) A uniform composition throughout.
B) Separable by filtration.
C) Distinct layers.
D) Chemically bonded components.
,Answer: A) A uniform composition throughout.
Rationale: A homogeneous mixture has a uniform composition
(e.g., saltwater), as opposed to a heterogeneous mixture which
has distinct parts (e.g., sand in water).
Atomic Structure & The Periodic Table
3. What is the atomic number of an element?
A) The number of neutrons in the nucleus.
B) The total mass of the atom.
C) The number of protons in the nucleus.
D) The number of electrons in the outer shell.
Answer: C) The number of protons in the nucleus.
Rationale: The atomic number (Z) defines the element and equals
the number of protons. In a neutral atom, this also equals the
number of electrons.
4. An atom of Carbon-14 contains how many neutrons?
A) 6
B) 7
C) 8
D) 12
Answer: C) 8
Rationale: Carbon has an atomic number of 6 (6 protons). The
mass number of Carbon-14 is 14. Neutrons = Mass Number -
Protons, so 14 - 6 = 8.
5. An atom of potassium has 19 protons and 20 neutrons.
What is its mass number?
A) 19
,B) 20
C) 39
D) 58
Answer: C) 39
Rationale: Mass number is the total number of protons and
neutrons in an atom's nucleus.
6. Which subatomic particle is responsible for chemical
bonding?
A) Proton
B) Neutron
C) Electron
D) Nucleus
Answer: C) Electron
Rationale: Electrons, specifically valence electrons in the
outermost shell, are involved in chemical bonding.
Chemical Bonding
7. What type of bond forms between sodium (Na) and
chlorine (Cl)?
A) Nonpolar covalent
B) Polar covalent
C) Ionic
D) Hydrogen
Answer: C) Ionic
Rationale: The large electronegativity difference between sodium
(a metal) and chlorine (a nonmetal) causes electron transfer,
resulting in an ionic bond.
, 8. Which compound is held together by covalent bonds?
A) NaCl
B) MgO
C) H₂O
D) CaF₂
Answer: C) H₂O
Rationale: Water is composed of nonmetals (hydrogen and
oxygen) held together by covalent bonds.
Chemical Reactions & Stoichiometry
9. What type of reaction is: 2KClO₃ → 2KCl + 3O₂?
A) Synthesis
B) Decomposition
C) Single replacement
D) Double replacement
Answer: B) Decomposition
Rationale: A single compound (KClO₃) breaks down into two or
more simpler substances (KCl and O₂).
Definitions & Key Concepts
10. The mass number of an atom is defined as:
A) The number of protons only.
B) The number of electrons only.
C) The number of neutrons only.
D) The number of protons plus neutrons.
Objective Assessment Actual Exam
2025/2026 | Questions with
Verified Answers with Rationale |
Guaranteed Pass |Graded A+
Elements, Compounds, and Mixtures
1. Which of the following is a compound?
A) Air
B) Sodium
C) Water
D) Gold
Answer: C) Water
Rationale: Water (H₂O) is a substance with a fixed composition of
two elements chemically bonded. Air is a mixture, and sodium
(Na) and gold (Au) are elements.
2. A homogeneous mixture is best described as having:
A) A uniform composition throughout.
B) Separable by filtration.
C) Distinct layers.
D) Chemically bonded components.
,Answer: A) A uniform composition throughout.
Rationale: A homogeneous mixture has a uniform composition
(e.g., saltwater), as opposed to a heterogeneous mixture which
has distinct parts (e.g., sand in water).
Atomic Structure & The Periodic Table
3. What is the atomic number of an element?
A) The number of neutrons in the nucleus.
B) The total mass of the atom.
C) The number of protons in the nucleus.
D) The number of electrons in the outer shell.
Answer: C) The number of protons in the nucleus.
Rationale: The atomic number (Z) defines the element and equals
the number of protons. In a neutral atom, this also equals the
number of electrons.
4. An atom of Carbon-14 contains how many neutrons?
A) 6
B) 7
C) 8
D) 12
Answer: C) 8
Rationale: Carbon has an atomic number of 6 (6 protons). The
mass number of Carbon-14 is 14. Neutrons = Mass Number -
Protons, so 14 - 6 = 8.
5. An atom of potassium has 19 protons and 20 neutrons.
What is its mass number?
A) 19
,B) 20
C) 39
D) 58
Answer: C) 39
Rationale: Mass number is the total number of protons and
neutrons in an atom's nucleus.
6. Which subatomic particle is responsible for chemical
bonding?
A) Proton
B) Neutron
C) Electron
D) Nucleus
Answer: C) Electron
Rationale: Electrons, specifically valence electrons in the
outermost shell, are involved in chemical bonding.
Chemical Bonding
7. What type of bond forms between sodium (Na) and
chlorine (Cl)?
A) Nonpolar covalent
B) Polar covalent
C) Ionic
D) Hydrogen
Answer: C) Ionic
Rationale: The large electronegativity difference between sodium
(a metal) and chlorine (a nonmetal) causes electron transfer,
resulting in an ionic bond.
, 8. Which compound is held together by covalent bonds?
A) NaCl
B) MgO
C) H₂O
D) CaF₂
Answer: C) H₂O
Rationale: Water is composed of nonmetals (hydrogen and
oxygen) held together by covalent bonds.
Chemical Reactions & Stoichiometry
9. What type of reaction is: 2KClO₃ → 2KCl + 3O₂?
A) Synthesis
B) Decomposition
C) Single replacement
D) Double replacement
Answer: B) Decomposition
Rationale: A single compound (KClO₃) breaks down into two or
more simpler substances (KCl and O₂).
Definitions & Key Concepts
10. The mass number of an atom is defined as:
A) The number of protons only.
B) The number of electrons only.
C) The number of neutrons only.
D) The number of protons plus neutrons.
