In the scientific method, what is a tentative explanation of observations that can be tested by further experiments?
Hypothesis
✓
Scientific law
Theory
Measurement
Correct Answer
Hypothesis
A hypothesis is a proposed, testable explanation that experiments can support or refute. A scientific law summarizes observed behavior without explaining it. A theory is a well-tested explanation backed by a large body of evidence, not a tentative guess. A measurement is a recorded observation, not an explanation.
Category: Scientific Method
Question 2
Which term describes a concise verbal or mathematical statement that summarizes a vast number of observations but does not explain why nature behaves that way?
Hypothesis
Scientific law
✓
Theory
Prediction
Correct Answer
Scientific law
A scientific law describes a consistent pattern in nature, often as an equation, without giving the underlying reason. A hypothesis is a tentative, testable explanation. A theory explains why something happens. A prediction is an expected outcome of an experiment, not a summary of many observations.
Category: Scientific Method
Question 3
Which description fits a sample of matter in the gas state?
Definite shape and definite volume
Definite volume but no definite shape
No definite shape and no definite volume
✓
Definite shape but no definite volume
Correct Answer
No definite shape and no definite volume
A gas expands to fill its container completely, so it takes both the shape and the volume of the container. Definite shape and definite volume describes a solid. Definite volume but no definite shape describes a liquid. Definite shape but no definite volume does not describe any ordinary state of matter.
Category: States of Matter
Question 4
Filtered air inside a sealed flask is best classified as which kind of matter?
Heterogeneous mixture
Compound
Element
Homogeneous mixture
✓
Correct Answer
Homogeneous mixture
Air is a mixture of gases, mainly nitrogen and oxygen, whose composition is uniform throughout once dust is removed. Heterogeneous mixture is wrong because filtered air shows no visibly different regions. Compound is wrong because the gases in air are not chemically combined in a fixed ratio. Element is wrong because air contains several different substances.
Category: Classification of Matter
Question 5
Which of these substances is a compound?
Water
✓
Air
Oxygen gas
Brass
Correct Answer
Water
Water is a pure substance made of hydrogen and oxygen chemically combined in a fixed ratio, so it is a compound. Air is a mixture of gases. Oxygen gas is an element. Brass is an alloy, a homogeneous mixture of copper and zinc.
Category: Classification of Matter
Question 6
Which property of a substance can be observed only by changing it into a different substance?
Density
Flammability
✓
Melting point
Color
Correct Answer
Flammability
Flammability is a chemical property because testing it requires burning the substance, which turns it into new substances. Density is a physical property found from mass and volume. Melting point is a physical property because melting does not change the substance's identity. Color is a physical property seen just by looking.
Category: Physical and Chemical Properties
Question 7
Which process is a chemical change?
Ice melting
Sugar dissolving in water
Iron rusting
✓
Glass breaking
Correct Answer
Iron rusting
When iron rusts it reacts with oxygen and water to form iron oxide, a new substance, so it is a chemical change. Ice melting only changes the physical state of water. Sugar dissolving in water forms a mixture from which the sugar can be recovered by evaporation. Glass breaking changes only the size and shape of the pieces.
Category: Physical and Chemical Properties
Question 8
Which property of a pure substance stays the same whether the sample is large or small?
Mass
Volume
Length
Boiling point
✓
Correct Answer
Boiling point
Boiling point is an intensive property: a drop and a full pot of the same pure liquid boil at the same temperature under the same pressure. Mass is extensive because a larger sample has more mass. Volume is extensive because a larger sample takes up more space. Length is extensive because it grows with the size of the sample.
Category: Physical and Chemical Properties
Question 9
What is the SI base unit of mass?
Kilogram
✓
Gram
Milligram
Pound
Correct Answer
Kilogram
The kilogram is the SI base unit of mass; it is the only base unit whose name includes a prefix. Gram is a common metric unit but equals one-thousandth of the base unit. Milligram is a smaller unit equal to one-thousandth of a gram. Pound is a unit of the English system, not the SI.
Category: SI Units and Prefixes
Question 10
The metric prefix milli- multiplies a unit by which factor?
0.01
0.001
✓
1000
0.000001
Correct Answer
0.001
Milli- means one-thousandth, so 1 millimeter is 0.001 meter. The value 0.01 is the factor for centi-. The value 1000 is the factor for kilo-. The value 0.000001 is the factor for micro-.
Category: SI Units and Prefixes
Question 11
A healthy human body temperature is 37 degrees Celsius. What is this temperature in K, rounded to the nearest whole number?
236 K
99 K
310 K
✓
37 K
Correct Answer
310 K
To convert from Celsius to the absolute scale, add 273.15, so 37 + 273.15 = 310.15, which rounds to 310 K. The value 236 K comes from subtracting 37 from 273 instead of adding. The value 99 K comes from applying the Fahrenheit conversion, 1.8 times 37 plus 32. The value 37 K ignores the offset between the two scales.
Category: SI Units and Prefixes
Question 12
One milliliter is exactly equal to which volume?
1 cubic decimeter
1 cubic meter
10 cubic centimeters
1 cubic centimeter
✓
Correct Answer
1 cubic centimeter
A milliliter is one-thousandth of a liter, and a liter is a cube 10 cm on a side, or 1000 cubic centimeters, so 1 mL equals 1 cubic centimeter. 1 cubic decimeter equals 1 liter, a thousand times larger. 1 cubic meter equals 1000 liters. 10 cubic centimeters equals 10 mL.
Category: SI Units and Prefixes
Question 13
A metal sample has a mass of 54.0 g and a volume of 20.0 mL. What is its density, to three significant figures?
2.70 g/mL
✓
0.370 g/mL
1080 g/mL
34.0 g/mL
Correct Answer
2.70 g/mL
Density is mass divided by volume: 54.0 g / 20.0 mL = 2.70 g/mL. The value 0.370 g/mL comes from dividing volume by mass. The value 1080 g/mL comes from multiplying mass by volume. The value 34.0 g/mL comes from subtracting volume from mass.
Category: Measurement Calculations
Question 14
How many significant figures are in the measured value 0.004050 g?
3
4
✓
7
2
Correct Answer
4
The leading zeros only locate the decimal point and are not significant, while the zero between 4 and 5 and the trailing zero after the decimal point are significant, giving 4 (the digits 4, 0, 5, 0). The answer 3 wrongly drops the trailing zero. The answer 7 wrongly counts every digit. The answer 2 counts only the nonzero digits.
Category: Significant Figures
Question 15
Two lengths, 12.52 cm and 3.1 cm, are added. How should the sum be reported with correct significant figures?
15.62 cm
16 cm
15.6 cm
✓
15.620 cm
Correct Answer
15.6 cm
In addition, the result keeps the same number of decimal places as the measurement with the fewest decimal places; 3.1 cm has one, so 15.62 rounds to 15.6 cm. The value 15.62 cm keeps too many decimal places. The value 16 cm rounds too far. The value 15.620 cm adds a digit that was never measured.
Category: Significant Figures
Question 16
A rectangle measures 4.56 cm by 1.4 cm. How should its area be reported with correct significant figures?
6.38 cm2
6.384 cm2
6 cm2
6.4 cm2
✓
Correct Answer
6.4 cm2
In multiplication, the result has as many significant figures as the factor with the fewest; 1.4 cm has two, so 6.384 rounds to 6.4 cm2. The value 6.38 cm2 keeps three significant figures. The value 6.384 cm2 is the unrounded calculator result. The value 6 cm2 keeps only one significant figure.
Category: Significant Figures
Question 17
Repeated measurements that agree closely with one another but are far from the true value are described as what?
Precise but not accurate
✓
Accurate but not precise
Accurate and precise
Neither accurate nor precise
Correct Answer
Precise but not accurate
Precision is how closely repeated measurements agree with each other, and accuracy is how close they are to the true value, so a tight cluster far from the true value is precise but not accurate. Accurate but not precise would mean scattered values that average near the true value. Accurate and precise would require the cluster to sit at the true value. Neither accurate nor precise would mean scattered values far from the true value.
Category: Accuracy and Precision
Question 18
Using the exact relationship 1 in = 2.54 cm, how many centimeters are in 3.00 in?
1.18 cm
7.62 cm
✓
0.847 cm
5.54 cm
Correct Answer
7.62 cm
Multiply by the conversion factor so inches cancel: 3.00 in x (2.54 cm / 1 in) = 7.62 cm. The value 1.18 cm comes from dividing 3.00 by 2.54, using the factor upside down. The value 0.847 cm comes from dividing 2.54 by 3.00. The value 5.54 cm comes from adding the numbers instead of multiplying.
Category: Measurement Calculations
Question 19
Which value is an exact number with unlimited significant figures?
A mass of 12.0 g read from a balance
A length of 12 cm measured with a ruler
The 12 eggs counted in a carton
✓
A volume of 12.00 mL read from a buret
Correct Answer
The 12 eggs counted in a carton
Numbers obtained by counting discrete objects, or set by definition, are exact and carry no uncertainty. A mass of 12.0 g read from a balance is a measurement with three significant figures. A length of 12 cm measured with a ruler is a measurement with two significant figures. A volume of 12.00 mL read from a buret is a measurement with four significant figures.
Category: Significant Figures
Question 20
An astronaut travels from Earth to the Moon. Which of these quantities is unchanged?
Her weight
Gravity acting on her
Her scale reading
Her mass
✓
Correct Answer
Her mass
Mass measures the amount of matter in an object and does not depend on location. Her weight is the force of gravity on her, which is smaller on the Moon. Gravity acting on her is weaker on the Moon because the Moon has less mass than Earth. Her scale reading reflects her weight, so it drops on the Moon.
Category: SI Units and Prefixes