WGU D425 — Introduction to Chemistry
Objective Assessment (OA) Exam
Questions with Answers| Latest Update| Guaranteed Pass
1. Which of the following is an example of a chemical property?
A. Density
B. Melting point
C. Flammability
D. Color
Answer: C. Flammability
Rationale: Flammability describes how a substance reacts (burns) when exposed to
oxygen, changing its composition. Density, melting point, and color are physical
properties observed without changing the substance's identity.
2. A sample of matter that has a definite volume but takes the shape of its container is
in which state?
A. Solid
B. Liquid
C. Gas
D. Plasma
Answer: B. Liquid
Rationale: Liquids have a fixed volume because particles are held close together by
intermolecular forces, but they flow and take the shape of their container because
those particles can move past one another.
3. Which of the following is a chemical change?
A. Dissolving sugar in water
B. Melting ice
C. Rusting of iron
D. Crushing a can
Answer: C. Rusting of iron
Rationale: Rusting is a chemical change because iron reacts with oxygen to form a
new substance, iron oxide. The other options are physical changes because no new
substance is formed.
,4. How many significant figures are in the measurement 0.004205 g?
A. 3
B. 4
C. 6
D. 7
Answer: B. 4
Rationale: Leading zeros are never significant. The significant digits are 4, 2, 0, and 5,
giving 4 significant figures.
5. Convert 45.0 °C to Kelvin.
A. 228.15 K
B. 318.15 K
C. 45.0 K
D. 273.15 K
Answer: B. 318.15 K
Rationale: K = °C + 273.15, so 45.0 + 273.15 = 318.15 K.
6. Which of the following best describes the difference between an element and a
compound?
A. An element can be broken down into simpler substances by chemical means, a
compound cannot
B. A compound is made of two or more elements chemically combined in fixed
proportions, while an element cannot be broken down further
C. Elements and compounds are the same thing
D. A compound is always a mixture of gases
Answer: B. A compound is made of two or more elements chemically combined in
fixed proportions, while an element cannot be broken down further
Rationale: An element is a pure substance made of only one type of atom, while a
compound consists of two or more elements chemically bonded together in a fixed
ratio and can be broken down chemically into its elements.
7. Which unit is the SI base unit for mass?
A. Gram
B. Pound
C. Kilogram
D. Milligram
Answer: C. Kilogram
, Rationale: The kilogram (kg) is the SI base unit of mass; the gram is a derived, more
commonly used subunit.
8. A homogeneous mixture is also known as a:
A. Compound
B. Solution
C. Suspension
D. Pure element
Answer: B. Solution
Rationale: A homogeneous mixture has uniform composition throughout and is called
a solution, such as salt water.
9. Using dimensional analysis, how many centimeters are in 3.5 meters?
A. 0.35 cm
B. 35 cm
C. 350 cm
D. 3500 cm
Answer: C. 350 cm
Rationale: Since 1 m = 100 cm, 3.5 m × 100 cm/m = 350 cm.
Atomic Structure
10. Which subatomic particle has a negative charge?
A. Proton
B. Neutron
C. Electron
D. Nucleon
Answer: C. Electron
Rationale: Electrons carry a negative charge and orbit the nucleus, while protons are
positive and neutrons are neutral.
11. The atomic number of an element represents the number of:
A. Neutrons in the nucleus
B. Protons in the nucleus
C. Electrons in the outer shell
D. Total nucleons
Objective Assessment (OA) Exam
Questions with Answers| Latest Update| Guaranteed Pass
1. Which of the following is an example of a chemical property?
A. Density
B. Melting point
C. Flammability
D. Color
Answer: C. Flammability
Rationale: Flammability describes how a substance reacts (burns) when exposed to
oxygen, changing its composition. Density, melting point, and color are physical
properties observed without changing the substance's identity.
2. A sample of matter that has a definite volume but takes the shape of its container is
in which state?
A. Solid
B. Liquid
C. Gas
D. Plasma
Answer: B. Liquid
Rationale: Liquids have a fixed volume because particles are held close together by
intermolecular forces, but they flow and take the shape of their container because
those particles can move past one another.
3. Which of the following is a chemical change?
A. Dissolving sugar in water
B. Melting ice
C. Rusting of iron
D. Crushing a can
Answer: C. Rusting of iron
Rationale: Rusting is a chemical change because iron reacts with oxygen to form a
new substance, iron oxide. The other options are physical changes because no new
substance is formed.
,4. How many significant figures are in the measurement 0.004205 g?
A. 3
B. 4
C. 6
D. 7
Answer: B. 4
Rationale: Leading zeros are never significant. The significant digits are 4, 2, 0, and 5,
giving 4 significant figures.
5. Convert 45.0 °C to Kelvin.
A. 228.15 K
B. 318.15 K
C. 45.0 K
D. 273.15 K
Answer: B. 318.15 K
Rationale: K = °C + 273.15, so 45.0 + 273.15 = 318.15 K.
6. Which of the following best describes the difference between an element and a
compound?
A. An element can be broken down into simpler substances by chemical means, a
compound cannot
B. A compound is made of two or more elements chemically combined in fixed
proportions, while an element cannot be broken down further
C. Elements and compounds are the same thing
D. A compound is always a mixture of gases
Answer: B. A compound is made of two or more elements chemically combined in
fixed proportions, while an element cannot be broken down further
Rationale: An element is a pure substance made of only one type of atom, while a
compound consists of two or more elements chemically bonded together in a fixed
ratio and can be broken down chemically into its elements.
7. Which unit is the SI base unit for mass?
A. Gram
B. Pound
C. Kilogram
D. Milligram
Answer: C. Kilogram
, Rationale: The kilogram (kg) is the SI base unit of mass; the gram is a derived, more
commonly used subunit.
8. A homogeneous mixture is also known as a:
A. Compound
B. Solution
C. Suspension
D. Pure element
Answer: B. Solution
Rationale: A homogeneous mixture has uniform composition throughout and is called
a solution, such as salt water.
9. Using dimensional analysis, how many centimeters are in 3.5 meters?
A. 0.35 cm
B. 35 cm
C. 350 cm
D. 3500 cm
Answer: C. 350 cm
Rationale: Since 1 m = 100 cm, 3.5 m × 100 cm/m = 350 cm.
Atomic Structure
10. Which subatomic particle has a negative charge?
A. Proton
B. Neutron
C. Electron
D. Nucleon
Answer: C. Electron
Rationale: Electrons carry a negative charge and orbit the nucleus, while protons are
positive and neutrons are neutral.
11. The atomic number of an element represents the number of:
A. Neutrons in the nucleus
B. Protons in the nucleus
C. Electrons in the outer shell
D. Total nucleons
