WGU D425
Introduction to Chemistry — Objective Assessment
Questions & Answers| Latest Update| Guaranteed Pass
,1. Which of the following is an example of a physical property of matter?
A. Flammability
B. Reactivity with acid
C. Boiling point
D. Ability to rust
Answer: C — Boiling point
Rationale: Boiling point is a physical property because it can be observed and
measured without changing the chemical identity of the substance. Flammability,
reactivity, and rusting are chemical properties, since they describe how a substance
changes into a different substance.
2. A chemical change is best identified by which of the following observations?
A. A change in state, such as melting
B. Formation of a new substance with different properties, such as gas bubbles or a
precipitate
C. A change in shape only
D. A change in temperature with no other evidence
Answer: B — Formation of a new substance with different properties, such as gas
bubbles or a precipitate
Rationale: Chemical changes produce new substances with different chemical
properties; evidence includes gas production, color change, precipitate formation, or
heat/light release, distinct from physical changes like melting or dissolving.
3. Which of the following is classified as a mixture rather than a pure substance?
A. Distilled water
B. Table salt (sodium chloride)
C. Salt water
D. Oxygen gas
Answer: C — Salt water
Rationale: Salt water is a mixture because it consists of two or more substances
(water and sodium chloride) that are physically combined and can be separated by
physical means, unlike pure substances such as distilled water, table salt, or oxygen
gas.
4. In the metric (SI) system, which prefix represents a factor of 10^-3?
A. kilo-
, B. centi-
C. milli-
D. mega-
Answer: C — milli-
Rationale: The prefix "milli-" represents one-thousandth (10^-3) of a base unit, so a
milligram is 0.001 gram; "kilo-" is 10^3, "centi-" is 10^-2, and "mega-" is 10^6.
5. How many significant figures are in the measurement 0.004520 grams?
A. Two
B. Three
C. Four
D. Seven
Answer: C — Four
Rationale: Leading zeros are never significant, but the digits 4, 5, and the trailing zero
after the decimal point (2, 0) are significant, giving four significant figures: 4, 5, 2, 0.
6. When adding or subtracting measured values, the answer should be rounded to
match:
A. The measurement with the most significant figures
B. The measurement with the fewest decimal places
C. The average number of significant figures
D. Always three significant figures
Answer: B — The measurement with the fewest decimal places
Rationale: For addition and subtraction, the result is rounded to the same number of
decimal places as the measurement with the fewest decimal places, since precision is
limited by the least precise measurement.
7. Density is calculated using which formula?
A. Mass divided by volume
B. Volume divided by mass
C. Mass multiplied by volume
D. Mass minus volume
Answer: A — Mass divided by volume
Rationale: Density (D) equals mass divided by volume (D = m/V), expressing how
much mass is contained in a given volume of a substance.
Introduction to Chemistry — Objective Assessment
Questions & Answers| Latest Update| Guaranteed Pass
,1. Which of the following is an example of a physical property of matter?
A. Flammability
B. Reactivity with acid
C. Boiling point
D. Ability to rust
Answer: C — Boiling point
Rationale: Boiling point is a physical property because it can be observed and
measured without changing the chemical identity of the substance. Flammability,
reactivity, and rusting are chemical properties, since they describe how a substance
changes into a different substance.
2. A chemical change is best identified by which of the following observations?
A. A change in state, such as melting
B. Formation of a new substance with different properties, such as gas bubbles or a
precipitate
C. A change in shape only
D. A change in temperature with no other evidence
Answer: B — Formation of a new substance with different properties, such as gas
bubbles or a precipitate
Rationale: Chemical changes produce new substances with different chemical
properties; evidence includes gas production, color change, precipitate formation, or
heat/light release, distinct from physical changes like melting or dissolving.
3. Which of the following is classified as a mixture rather than a pure substance?
A. Distilled water
B. Table salt (sodium chloride)
C. Salt water
D. Oxygen gas
Answer: C — Salt water
Rationale: Salt water is a mixture because it consists of two or more substances
(water and sodium chloride) that are physically combined and can be separated by
physical means, unlike pure substances such as distilled water, table salt, or oxygen
gas.
4. In the metric (SI) system, which prefix represents a factor of 10^-3?
A. kilo-
, B. centi-
C. milli-
D. mega-
Answer: C — milli-
Rationale: The prefix "milli-" represents one-thousandth (10^-3) of a base unit, so a
milligram is 0.001 gram; "kilo-" is 10^3, "centi-" is 10^-2, and "mega-" is 10^6.
5. How many significant figures are in the measurement 0.004520 grams?
A. Two
B. Three
C. Four
D. Seven
Answer: C — Four
Rationale: Leading zeros are never significant, but the digits 4, 5, and the trailing zero
after the decimal point (2, 0) are significant, giving four significant figures: 4, 5, 2, 0.
6. When adding or subtracting measured values, the answer should be rounded to
match:
A. The measurement with the most significant figures
B. The measurement with the fewest decimal places
C. The average number of significant figures
D. Always three significant figures
Answer: B — The measurement with the fewest decimal places
Rationale: For addition and subtraction, the result is rounded to the same number of
decimal places as the measurement with the fewest decimal places, since precision is
limited by the least precise measurement.
7. Density is calculated using which formula?
A. Mass divided by volume
B. Volume divided by mass
C. Mass multiplied by volume
D. Mass minus volume
Answer: A — Mass divided by volume
Rationale: Density (D) equals mass divided by volume (D = m/V), expressing how
much mass is contained in a given volume of a substance.
