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Grade 7 Science and Technology study materials
Grade 7 Science and Technology study resources

Grade 7 Science and Technology practice questions

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Question 1Scientific Inquiry and Investigation Skills

A student wants to know whether adding salt to water changes how fast it boils. Which statement is the best testable hypothesis for this investigation?

  1. Salt makes water taste different from pure water.
  2. Salt is a compound made of sodium and chlorine.
  3. Adding salt to water makes it boil at a higher temperature than pure water. Correct answer.
  4. Water boils when it gets hot enough.

Explanation

A testable hypothesis must predict a measurable relationship between a manipulated variable and an outcome. Option 0 links salt amount to boiling temperature, which can be measured with a thermometer. The other statements are facts or observations that cannot be tested as a predicted relationship.

Question 2Scientific Inquiry and Investigation Skills

During an experiment, a group records the length of a bean seedling every day for two weeks. What type of variable is the length of the seedling?

  1. Independent variable
  2. Constant condition
  3. Dependent variable Correct answer.
  4. Controlled variable

Explanation

The dependent variable is the factor that is measured in response to changes the investigator makes. Seedling length is recorded as the outcome, so it depends on the conditions set up in the investigation. Controlled variables and constants are the factors kept the same.

Question 3Scientific Inquiry and Investigation Skills

A student measures the mass of a metal block three times and gets 24.1 g, 24.2 g, and 24.0 g. The true mass is 24.1 g. Which statement best describes these measurements?

  1. They are both accurate and precise. Correct answer.
  2. They are precise but not accurate.
  3. They are neither accurate nor precise.
  4. They are accurate but not precise.

Explanation

Precision means repeated measurements are close to each other, while accuracy means they are close to the true value. These readings cluster tightly around 24.1 g, which is also the true mass. The measurements therefore meet both criteria.

Question 4Scientific Inquiry and Investigation Skills

Which action is the most important safety step before a class investigation that involves heating a liquid over a Bunsen burner?

  1. Tying back loose hair and wearing safety goggles Correct answer.
  2. Recording the starting temperature of the liquid
  3. Choosing the largest beaker available
  4. Labelling the beaker with the group name

Explanation

Flame and hot-liquid investigations require protecting the body from burns and the eyes from splashes. Tying back loose hair and wearing goggles addresses those hazards directly. Recording data and labelling equipment are useful but do not reduce the physical risk.

Question 5Scientific Inquiry and Investigation Skills

A student uses a ruler marked in millimetres to measure the length of a leaf. Which reading is recorded to the correct level of precision?

  1. 7 cm
  2. 7.4 cm Correct answer.
  3. 7.45 cm
  4. 7.453 cm

Explanation

A ruler marked in millimetres allows a reading to the nearest 0.1 cm, with one estimated digit. Recording 7.4 cm matches that precision. Extra decimal places suggest precision the instrument cannot provide.

Question 6Scientific Inquiry and Investigation Skills

In an investigation, a student places one identical potted plant in each of four rooms with different light levels and waters them equally. Why does the student use four plants rather than one?

  1. To make the experiment finish faster
  2. To reduce the effect of natural variation between plants Correct answer.
  3. To avoid needing a control group
  4. To increase the number of independent variables

Explanation

Living organisms vary naturally, so a single plant could give a misleading result by chance. Repeating with several identical plants helps average out that natural variation. Replication does not change the number of independent variables or replace a control.

Question 7Scientific Inquiry and Investigation Skills

A group tests how the height of a ramp affects how far a toy car rolls. They change the ramp height and measure the distance the car travels. Which factor must be kept constant for a fair test?

  1. The height of the ramp
  2. The length of the ramp
  3. The mass of the car Correct answer.
  4. The distance the car travels

Explanation

A fair test changes only one variable at a time, so all other factors that could affect the result must be held constant. The car's mass affects how far it rolls, so it must stay the same for every trial. Ramp height is the variable being changed, and distance is the measured outcome.

Question 8Scientific Inquiry and Investigation Skills

A student claims that a fertiliser makes plants grow taller. The class wants to check whether the result is reliable. Which action best supports reliability?

  1. Ask the student to describe the result in more detail
  2. Repeat the investigation several times and compare the results Correct answer.
  3. Use a taller plant species for the second trial
  4. Increase the amount of fertiliser used in the second trial

Explanation

Reliability refers to whether the same result is obtained consistently when the investigation is repeated. Repeating the procedure and comparing outcomes tests that consistency. Changing the species, the dose, or the description does not check whether the original result repeats.

Question 9Scientific Inquiry and Investigation Skills

A student wants to find out whether different liquids freeze at different temperatures. Which equipment is essential to collect valid data?

  1. A thermometer and identical containers for each liquid Correct answer.
  2. A balance and a ruler
  3. A stopwatch and a measuring cylinder
  4. A microscope and glass slides

Explanation

The investigation measures the temperature at which each liquid freezes, so a thermometer is essential. Identical containers ensure each liquid is tested under the same conditions. Other equipment does not measure freezing temperature.

Question 10Scientific Inquiry and Investigation Skills

A class surveys students about how many hours they sleep each night. Which method produces the most reliable data?

  1. Asking a few friends in one class
  2. Estimating the average from memory
  3. Asking only students who arrive early
  4. Recording answers from a large random sample of students Correct answer.

Explanation

A large random sample is more likely to represent the whole student population and reduces the influence of unusual individuals. Small or biased groups can distort the average. Memory estimates are not recorded measurements.

Question 11Scientific Inquiry and Investigation Skills

A student writes: 'If a ball is dropped from a greater height, then it will bounce higher.' Which part of this statement is the prediction being tested?

  1. The ball is made of rubber.
  2. The height of the drop.
  3. The ball is dropped.
  4. The ball will bounce higher. Correct answer.

Explanation

In an if-then hypothesis, the 'then' part states the predicted outcome that the investigation will test. Here the predicted outcome is a higher bounce. The drop height is the manipulated variable, and the ball's material is not part of the statement.

Question 12Scientific Inquiry and Investigation Skills

Two students measure the same book's mass on the same balance and get 512 g and 498 g. What is the most reasonable interpretation?

  1. The balance is accurate but not precise.
  2. The book's mass changed between readings.
  3. The measurements show large random error and should be repeated. Correct answer.
  4. The true mass is exactly 505 g.

Explanation

A 14 g difference between repeated readings on the same instrument suggests random error such as misreading or an unstable balance. Repeating the measurement is the appropriate response. The data do not justify claiming an exact true value or a real change in mass.

Question 13Scientific Inquiry and Investigation Skills

A student graphs results from an investigation and finds that as the temperature of water increases, the amount of sugar that dissolves also increases. What type of relationship does the graph show?

  1. A random pattern
  2. A positive correlation Correct answer.
  3. No relationship
  4. A negative correlation

Explanation

A positive correlation occurs when both variables increase together. Here, higher temperature is paired with more dissolved sugar. A negative correlation would mean one variable falls as the other rises.

Question 14Scientific Inquiry and Investigation Skills

A group records the following results for a plant's height over four weeks: 2 cm, 5 cm, 7 cm, 12 cm. Which conclusion is best supported by these data?

  1. The plant grew at a constant rate each week.
  2. The plant stopped growing after week two.
  3. The plant's growth was caused by the type of soil.
  4. The plant grew every week but at different rates. Correct answer.

Explanation

The height increases every week, so growth occurred throughout, but the weekly increases (3, 2, and 5 cm) differ. The data therefore support steady growth at a variable rate. They cannot establish a constant rate or identify soil as the cause.

Question 15Scientific Inquiry and Investigation Skills

A student tests whether the colour of light affects how quickly a plant grows. Which is the independent variable in this investigation?

  1. The colour of light Correct answer.
  2. The height of the plant
  3. The type of plant used
  4. The amount of water given

Explanation

The independent variable is the factor the investigator deliberately changes. Since the student chooses different light colours, that is the independent variable. Plant height is the measured outcome, and water and plant type are controlled.

Question 16Scientific Inquiry and Investigation Skills

A student predicts that a paper aeroplane with wider wings will travel farther. The results show no clear pattern. What is the most scientific response?

  1. Report only the trials that support the prediction
  2. Repeat the investigation and check whether the method was consistent Correct answer.
  3. Discard the results and keep the original prediction
  4. Change the prediction to match the results

Explanation

Unexpected results should prompt a check of the method and repetition before conclusions are drawn. Inconsistency in throwing, measuring, or materials could explain the lack of pattern. Adjusting predictions to fit data or hiding contradictory trials is not honest scientific practice.

Question 17Scientific Inquiry and Investigation Skills

Which statement describes a scientific model's main purpose?

  1. To prove that a hypothesis is true
  2. To represent an object or process in a simplified way that can be tested and revised Correct answer.
  3. To provide an exact copy of a real object
  4. To replace the need for experiments

Explanation

Models simplify complex systems so scientists can explain, predict, and test ideas. Because they are simplified, models are revised as new evidence appears. They support experiments rather than replace them or guarantee proof.

Question 18Scientific Inquiry and Investigation Skills

A student measures the volume of a stone by placing it in a measuring cylinder of water. The water level rises from 40 mL to 55 mL. What is the volume of the stone?

  1. 15 mL Correct answer.
  2. 55 mL
  3. 95 mL
  4. 40 mL

Explanation

The displacement method gives the object's volume as the difference between the final and initial water levels. Subtracting 40 mL from 55 mL gives 15 mL. Adding the readings would be incorrect because the initial water was already present.

Question 19Scientific Inquiry and Investigation Skills

In a controlled experiment, what is the main function of a control group?

  1. To test several variables at once
  2. To make the results look more convincing
  3. To provide a baseline for comparison without the treatment Correct answer.
  4. To increase the number of trials

Explanation

A control group is treated the same as the experimental group except that it does not receive the variable being tested. Comparing the two shows whether the treatment caused any change. It does not increase trials or allow multiple variables.

Question 20Scientific Inquiry and Investigation Skills

A class wants to investigate whether the type of surface affects how far a ball rolls. Which set of conditions makes the test fair?

  1. Different balls and same push, different surfaces
  2. Different balls and different pushes, same surface
  3. Same ball and same push, different surfaces Correct answer.
  4. Same ball and same push, same surface

Explanation

A fair test changes only the independent variable, which here is the surface type. The ball and the push must therefore stay the same for every trial. Changing the ball or the push would introduce extra variables.

Question 21Scientific Inquiry and Investigation Skills

A student concludes that a new fertiliser caused plants to grow taller because the treated plants were taller than untreated plants. Which additional information would most strengthen this conclusion?

  1. The treated and untreated plants were otherwise kept under identical conditions Correct answer.
  2. The treated plants were also given more water
  3. The treated plants were grown in a warmer room
  4. The treated plants were a different species

Explanation

A causal conclusion is strongest when only the treatment differs between groups. Identical conditions rule out alternative explanations such as water, temperature, or species. If other factors also differed, the cause of the growth would be uncertain.

Question 22Scientific Inquiry and Investigation Skills

A graph shows data points that are scattered with no clear trend. Which statement best describes the relationship?

  1. There is a strong positive correlation
  2. There is no clear correlation between the variables Correct answer.
  3. There is a strong negative correlation
  4. The independent variable causes the dependent variable

Explanation

A scatter with no visible pattern indicates no clear correlation between the variables. Correlation also does not by itself establish causation. A strong correlation would require points to follow a clear upward or downward trend.

Question 23Scientific Inquiry and Investigation Skills

A student wants to determine whether temperature affects the rate at which sugar dissolves. Which measurement plan is best?

  1. Use different amounts of sugar at each temperature
  2. Stir only the warmest samples
  3. Time how long a fixed amount of sugar takes to dissolve in water at several temperatures Correct answer.
  4. Change the amount of water for each trial

Explanation

To isolate temperature as the cause, the amount of sugar, the water volume, and the stirring must stay the same while temperature is varied. Timing dissolution at several temperatures then reveals the effect. Varying sugar, stirring, or water adds confounding factors.

Question 24Scientific Inquiry and Investigation Skills

A student repeats a measurement five times and calculates the average. Why is reporting the average useful?

  1. It guarantees the result is accurate
  2. It removes the need to record individual values
  3. It makes the experiment a fair test
  4. It reduces the influence of random errors in individual readings Correct answer.

Explanation

Random errors can push individual readings above or below the true value, and averaging tends to balance these out. However, averaging does not correct systematic errors or guarantee accuracy. Individual values should still be recorded.

Question 25Scientific Inquiry and Investigation Skills

A student claims that ice melts faster in salty water than in pure water based on one trial. Which criticism of this conclusion is most valid?

  1. The investigation used water, so it cannot measure melting
  2. Ice always melts at the same rate
  3. A single trial may not be reliable, so it should be repeated Correct answer.
  4. Salt has no effect on any physical process

Explanation

A conclusion drawn from one trial may reflect chance or an unnoticed error, so replication is needed to check reliability. The other criticisms misstate the science or dismiss the investigation without evidence. Repeating the trial tests whether the pattern holds.

Question 26Scientific Inquiry and Investigation Skills

A student wants to know how the volume of a gas changes when it is cooled. Which observation would be the dependent variable in this investigation?

  1. The time of day the readings are taken
  2. The type of container holding the gas
  3. The volume reading of the gas Correct answer.
  4. The temperature to which the gas is cooled

Explanation

The dependent variable is the quantity that responds to the change the investigator makes, so it is what gets measured. Here the volume is measured after each cooling step, so it responds to temperature. Temperature is deliberately changed, making it the independent variable.

Question 27Scientific Inquiry and Investigation Skills

A group investigates whether the number of seeds in a pot affects how tall the seedlings grow. They plant pots with 1, 3, 5 and 7 seeds, give all pots the same soil, water and light, and measure the tallest seedling after three weeks. Which statement best identifies what is being kept constant?

  1. The height of the tallest seedling
  2. The soil, water and light given to each pot Correct answer.
  3. The number of pots used in the trial
  4. The number of seeds in each pot

Explanation

Controlled variables are the conditions held identical across all trials so that only the tested factor differs. Soil, water and light are the same for every pot, so they are the constants. The seed number is the factor being changed, and seedling height is the measured outcome.

Question 28Scientific Inquiry and Investigation Skills

A student records the temperature of a cooling cup of water every minute for ten minutes and plots the readings. Which type of graph is most appropriate for displaying how temperature changes over time?

  1. A line graph Correct answer.
  2. A pie chart
  3. A table of counts
  4. A bar chart

Explanation

A line graph shows how a continuous measured quantity changes across a continuous variable such as time, making trends visible. Temperature over time is continuous data on both axes. Pie charts and bar charts suit parts of a whole or separate categories, not a continuous trend.

Question 29Scientific Inquiry and Investigation Skills

Before starting an investigation with heating and glassware, a class reviews the safety rules. Which action best follows standard laboratory safety practice?

  1. Pointing a heated test tube towards a partner
  2. Tasting a solution to identify whether it is acidic
  3. Wearing safety goggles and tying back long hair Correct answer.
  4. Smelling a hot liquid by placing the nose directly over it

Explanation

Safety goggles protect the eyes from splashes and fumes, and tying back hair prevents it catching fire or dipping into chemicals. These precautions are standard whenever heat or glassware is used. The other actions expose people to injury or contamination.

Question 30Scientific Inquiry and Investigation Skills

A student measures the length of a pencil three times and records 12.4 cm, 12.5 cm and 12.4 cm. A classmate measures the same pencil once and records 14.2 cm. Which statement best interprets these results?

  1. The student's readings must be wrong because they are all similar
  2. The student's readings are precise and consistent, while the classmate's single reading is likely an error Correct answer.
  3. All four readings are equally reliable because a ruler was used
  4. The classmate's reading is more accurate because it was taken later

Explanation

Repeated readings that cluster closely together show good precision, and agreement between them suggests the value is dependable. A single value far from that cluster is likely a measurement error such as misreading the scale. Precision and accuracy are judged from repeated, careful measurement.

Question 31Scientific Inquiry and Investigation Skills

Two teams test whether a paper helicopter's wing length affects its falling time. Team A drops each helicopter once. Team B drops each helicopter five times and uses the mean falling time. Why does Team B's method give more trustworthy conclusions?

  1. Because Team B uses more paper than Team A
  2. Because repeated trials reduce the effect of random variation on the result Correct answer.
  3. Because five trials guarantee that the hypothesis is correct
  4. Because taking a mean removes the need to control other variables

Explanation

Random variation, such as slight differences in release or air movement, can shift any single measurement. Averaging several trials smooths out this scatter so the underlying pattern is clearer. Repetition improves reliability but does not remove the need for controlled variables.

Question 32Scientific Inquiry and Investigation Skills

A student wants to test whether the type of liquid affects how quickly a stain spreads through paper. Which plan gives the fairest test?

  1. Use a different paper size for each liquid and time each spread
  2. Use the same paper type, size and volume of each liquid, and time each spread Correct answer.
  3. Use one liquid only and repeat the test several times
  4. Change both the liquid type and the paper type for each trial

Explanation

A fair test changes only the independent variable, which here is the liquid type. Paper type, paper size and liquid volume must therefore be held constant so any difference in spread time can be attributed to the liquid. Timing the spread provides the dependent variable.

Question 33Scientific Inquiry and Investigation Skills

A student measures the mass of a sample on a balance and records 24 g. The true mass is 20 g. Which statement about this result is correct?

  1. The measurement is 4 g above the true mass, and precision cannot be assessed from a single reading Correct answer.
  2. The measurement can be neither accurate nor precise from a single reading
  3. The measurement is accurate but not precise
  4. The measurement is both accurate and precise

Explanation

The reading has an error of 24 − 20 = +4 g, or 20% of the true mass. Accuracy concerns closeness to the true value. Precision concerns agreement between repeated readings, so this single measurement cannot establish precision.

Question 34Scientific Inquiry and Investigation Skills

A student writes the hypothesis: 'If the surface of a ramp is rougher, then a block will slide down it more slowly.' Which statement correctly identifies the variables in this hypothesis?

  1. Ramp roughness is the dependent variable and the block's mass is the independent variable
  2. Both ramp roughness and sliding speed are controlled variables
  3. Ramp roughness is the independent variable and sliding speed is the dependent variable Correct answer.
  4. Sliding speed is the independent variable and ramp roughness is the dependent variable

Explanation

The hypothesis proposes that changing roughness causes a change in sliding speed. The factor deliberately changed is the independent variable, so roughness is independent. The factor expected to respond, sliding speed, is the dependent variable.

Question 35Scientific Inquiry and Investigation Skills

A class wants to find out whether students in their school prefer reading on paper or on a screen. Which sampling method is most likely to give a representative result?

  1. Ask the students who volunteer to answer a lunchtime survey
  2. Ask only students in one science class
  3. Select students at random from every year group in the school Correct answer.
  4. Ask only the members of the school book club

Explanation

A representative sample must reflect the whole population being studied, which here is all students in the school. Random selection across every year group reduces bias from any single group. Samples drawn from one club, one class or only volunteers tend to over-represent particular views.

Question 36Scientific Inquiry and Investigation Skills

A group measures the boiling point of water four times and obtains 98 °C, 99 °C, 98 °C and 99 °C. The accepted value is 100 °C. Which conclusion is best supported?

  1. The readings prove that water boils at 98 °C
  2. The readings are consistent with each other but slightly lower than the accepted value Correct answer.
  3. The readings are random and show no pattern
  4. The readings are invalid because they were repeated four times

Explanation

The four readings cluster tightly within one degree, which shows good consistency between trials. However, all lie slightly below the accepted value, suggesting a small systematic effect such as reduced air pressure or an instrument offset. Consistency alone does not make the readings match the accepted value.

Question 37Scientific Inquiry and Investigation Skills

During an investigation, a student notices that one data point lies far away from all the others. What is the most appropriate first step?

  1. Delete the point so the graph looks neater
  2. Ignore all the data and start a new investigation
  3. Change the point to match the trend of the other data
  4. Check the original records and repeat the measurement to see whether an error occurred Correct answer.

Explanation

An outlier may result from a recording mistake, an instrument fault or a genuine unusual event. Checking the records and repeating the measurement establishes which explanation is correct before any decision is made. Removing or altering data without checking is a form of dishonesty.

Question 38Scientific Inquiry and Investigation Skills

A student designs an investigation to test whether the concentration of salt solution affects the time taken for an ice cube to melt. The student plans to use ice cubes of different sizes to make the test more interesting. Why does this plan weaken the investigation?

  1. Because salt solution cannot be measured in a laboratory
  2. Because the dependent variable has not been identified
  3. Because ice cubes melt too quickly to be timed accurately
  4. Because changing ice cube size as well as salt concentration makes the cause of any difference unclear Correct answer.

Explanation

A valid investigation changes only one factor at a time. If ice cube size varies along with salt concentration, any difference in melting time could be due to either factor, so no clear conclusion is possible. Ice size should therefore be held constant.

Question 39Scientific Inquiry and Investigation Skills

A student claims that plants grow taller when watered with tea because the three tea-watered plants were taller than the three water-only plants. Which additional evidence would most strengthen this conclusion?

  1. A statement from a friend who also waters plants with tea
  2. A photograph of the tallest tea-watered plant
  3. Measuring the plants only at the end of the investigation
  4. Repeating the investigation several times with more plants and obtaining the same pattern Correct answer.

Explanation

A conclusion is strengthened when the same pattern appears consistently across repeated trials with larger samples. Repetition and increased sample size reduce the chance that the result arose from random variation. Anecdotes and single photographs do not provide this kind of support.

Question 40Scientific Inquiry and Investigation Skills

Two investigations examine the same question about how light intensity affects the rate of photosynthesis in pondweed. Investigation 1 counts bubbles for 30 seconds at each distance. Investigation 2 counts bubbles for 5 minutes at each distance and repeats each count three times. Which statement best compares the trustworthiness of the two sets of results?

  1. Both are equally trustworthy because both count bubbles at different distances
  2. Investigation 1 is more trustworthy because it takes less time and so has fewer chances for error
  3. Investigation 1 is more trustworthy because it uses a shorter counting period
  4. Investigation 2 is more trustworthy because longer counting periods and repeated trials reduce the effect of random variation Correct answer.

Explanation

Longer counting periods average out short-term fluctuations, and repeated trials show whether the pattern is consistent. Together these reduce the influence of random variation on the conclusion. A short single count is more easily distorted by chance events such as a brief change in light or temperature.

Question 41Matter, Materials and Their Properties

A student places a small stone on a balance and records its mass as 24 g. The stone is then crushed into powder. What is the mass of the powder?

  1. More than 24 g, because the surface area of the material increases
  2. 24 g, because crushing changes only the shape and size of the material Correct answer.
  3. It cannot be predicted without knowing the size of each powder grain
  4. Less than 24 g, because powder particles are smaller and lighter

Explanation

Mass is conserved when a material is broken into smaller pieces; crushing changes particle size and shape but not the total amount of matter. The powder contains exactly the same particles as the original stone, so the total mass stays 24 g. Surface area increases, but surface area is not mass.

Question 42Matter, Materials and Their Properties

Which property of a material is measured in grams per cubic centimetre (g/cm³)?

  1. Volume
  2. Density Correct answer.
  3. Weight
  4. Solubility

Explanation

Density is mass per unit volume, so its units are a mass unit divided by a volume unit, such as g/cm³. Volume alone is measured in cm³ and weight is a force measured in newtons. Solubility is measured as the mass of solute that dissolves in a given amount of solvent.

Question 43Matter, Materials and Their Properties

A clear liquid is poured into a glass. It takes the shape of the glass and forms a flat surface at the top. Which statement best explains these observations?

  1. The particles of a liquid are far apart and move freely in all directions
  2. The particles of a liquid are close together but can slide past one another Correct answer.
  3. The particles of a liquid are fixed in a rigid lattice and cannot move
  4. The particles of a liquid have no attractive forces between them

Explanation

In a liquid, particles are still close together and attracted to each other, but they are not locked in fixed positions, so the liquid flows and takes the container's shape. Because the particles remain close, the liquid keeps a nearly constant volume and forms a level surface. A rigid lattice describes a solid, and widely spaced free-moving particles describe a gas.

Question 44Matter, Materials and Their Properties

Which change of state involves particles gaining energy and moving from a liquid into a gas?

  1. Evaporation Correct answer.
  2. Freezing
  3. Deposition
  4. Condensation

Explanation

Evaporation is the change from liquid to gas, and it requires particles at the surface to gain enough energy to escape the liquid. Condensation is the reverse change, gas to liquid, and freezing is liquid to solid. Deposition is gas changing directly to solid.

Question 45Matter, Materials and Their Properties

A mixture of iron filings and sulfur powder is stirred together. Which property makes it possible to separate the two substances with a magnet?

  1. Iron is magnetic while sulfur is not Correct answer.
  2. Iron melts at a lower temperature than sulfur
  3. Sulfur dissolves in water while iron does not
  4. Iron is denser than sulfur

Explanation

Iron is attracted to a magnet and sulfur is not, so a magnet lifts the iron filings out of the mixture without changing either substance. The other properties listed do not involve magnetism and would not allow magnetic separation. Density differences would suit settling or flotation, not a magnet.

Question 46Matter, Materials and Their Properties

Which of the following is a chemical change rather than a physical change?

  1. Glass shattering on the floor
  2. Sugar dissolving in water
  3. A nail rusting in damp air Correct answer.
  4. Ice melting in a warm room

Explanation

Rusting forms a new substance, iron oxide, with properties different from the iron, so it is a chemical change and is difficult to reverse. Melting, dissolving and shattering change only the state, arrangement or size of the same substance. Those are physical changes that can be reversed without producing a new material.

Question 47Matter, Materials and Their Properties

A student tests an unknown solid with a circuit containing a battery and a small bulb. The bulb lights when the solid is placed in the gap. What does this show about the solid?

  1. It is transparent to light
  2. It is a thermal insulator
  3. It conducts electricity Correct answer.
  4. It is magnetic

Explanation

A material that completes the circuit and makes the bulb light allows electric charge to flow through it, so it is an electrical conductor. Thermal insulation, transparency and magnetism are separate properties tested in different ways. Only the flow of charge explains the lit bulb.

Question 48Matter, Materials and Their Properties

Which statement correctly describes the particles in a solid?

  1. They are spread far apart with large empty spaces between them
  2. They vibrate about fixed positions and are packed closely together Correct answer.
  3. They are arranged randomly and change position constantly
  4. They move freely through the whole volume of the material

Explanation

In a solid, particles are held close together in a regular arrangement and can only vibrate around fixed positions, which is why a solid keeps its own shape and volume. Free movement through the whole volume describes a gas, and constant random rearrangement describes a liquid.

Question 49Matter, Materials and Their Properties

A block has a mass of 180 g and a volume of 60 cm³. What is its density?

  1. 10 800 g/cm³
  2. 0.33 g/cm³
  3. 120 g/cm³
  4. 3 g/cm³ Correct answer.

Explanation

Density is calculated by dividing mass by volume, so 180 g divided by 60 cm³ gives 3 g/cm³. The value means each cubic centimetre of the block has a mass of about 3 g. Multiplying instead of dividing, or subtracting, gives the wrong answers.

Question 50Matter, Materials and Their Properties

Two liquids that do not mix are poured into a jar. Liquid X has a density of 0.8 g/cm³ and liquid Y has a density of 1.2 g/cm³. After the jar is left standing, what is observed?

  1. Liquid Y floats on top of liquid X
  2. The two liquids blend into a single layer
  3. Liquid X floats on top of liquid Y Correct answer.
  4. Both liquids sink and form a layer at the bottom

Explanation

When two immiscible liquids are placed together, the less dense liquid settles above the denser one. Liquid X has the lower density, so it forms the upper layer while liquid Y forms the lower layer. Blending would require the liquids to be miscible, which the question rules out.