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ICAS Science practice questions

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Question 1Observing & Measuring

Which unit is used in the International System of Units (SI) to measure length?

  1. metre Correct answer.
  2. litre
  3. gram
  4. second

Explanation

The metre is the SI base unit of length, and all other length units are defined from it. The litre measures volume, the gram measures mass and the second measures time.

Question 2Observing & Measuring

A student needs to find the mass of a rock. Which instrument should be used?

  1. A beam balance Correct answer.
  2. A ruler
  3. A thermometer
  4. A measuring cylinder

Explanation

Mass is measured with a balance, which compares the object against known masses. Measuring cylinders measure volume, thermometers measure temperature and rulers measure length.

Question 3Observing & Measuring

Which unit is the SI base unit for thermodynamic temperature?

  1. joule
  2. degree Celsius
  3. degree Fahrenheit
  4. kelvin Correct answer.

Explanation

The kelvin is the SI base unit of thermodynamic temperature. Degrees Celsius and degrees Fahrenheit are non-SI scales, and the joule is a unit of energy.

Question 4Observing & Measuring

A ruler is placed along a pencil. The left end of the pencil is at the 2.0 cm mark and the right end is at the 7.5 cm mark. What is the length of the pencil?

  1. 2.0 cm
  2. 7.5 cm
  3. 5.5 cm Correct answer.
  4. 9.5 cm

Explanation

Length is found by subtracting the starting mark from the end mark: 7.5 − 2.0 = 5.5 cm. Reading only the end mark would overstate the length by the starting offset.

Question 5Observing & Measuring

Which of these is a quantitative observation?

  1. The leaf smells minty.
  2. The leaf feels smooth.
  3. The leaf is green.
  4. The leaf is 6 cm long. Correct answer.

Explanation

A quantitative observation includes a number and a unit, such as a length of 6 cm. Colour, texture and smell are qualitative descriptions made without measurement.

Question 6Observing & Measuring

Which piece of equipment is designed to measure the volume of a liquid?

  1. A thermometer
  2. A stopwatch
  3. A measuring cylinder Correct answer.
  4. A beam balance for mass

Explanation

A measuring cylinder carries a graduated scale and is built for reading liquid volumes. Balances, thermometers and stopwatches measure other quantities.

Question 7Observing & Measuring

Which instrument is used to measure a time interval in an experiment?

  1. Ruler
  2. Stopwatch Correct answer.
  3. Balance
  4. Thermometer

Explanation

A stopwatch measures time intervals, often to 0.01 s. Thermometers, balances and rulers measure temperature, mass and length respectively.

Question 8Observing & Measuring

The prefix 'kilo' means:

  1. one million
  2. one hundredth
  3. one thousand Correct answer.
  4. one hundred

Explanation

The prefix kilo- means one thousand, so 1 kilometre equals 1000 metres. Centi- means one hundredth and milli- means one thousandth.

Question 9Observing & Measuring

When reading the volume of water in a measuring cylinder, how should the reading be taken?

  1. From below, at the top of the curve
  2. From above, at the top of the curve
  3. At eye level, bottom of the curve Correct answer.
  4. From any angle, at the middle

Explanation

The meniscus is the curved liquid surface, which for water dips at the edges, so the bottom of the curve is read. The eye must be level with the meniscus to avoid parallax error.

Question 10Observing & Measuring

A student reads a thermometer while looking at it from an angle. What type of error does this cause?

  1. A zero error
  2. A parallax error Correct answer.
  3. A scale error
  4. A calibration error

Explanation

Parallax error occurs when the scale and the pointer or meniscus are viewed from an angle, so the apparent reading is shifted. Viewing straight on at eye level removes this effect.

Question 11Observing & Measuring

A balance reads 0.4 g when nothing is placed on it. What should the student do to the readings?

  1. Ignore the offset
  2. Subtract the offset Correct answer.
  3. Replace the balance
  4. Add 0.4 g to each result

Explanation

A balance reading 0.4 g with nothing on it has a zero error, and the same offset appears in every measurement. Subtracting that offset corrects each reading.

Question 12Observing & Measuring

Three measurements of a length are 4.2 cm, 4.3 cm and 4.4 cm. What is the mean of these measurements?

  1. 4.2 cm
  2. 4.3 cm Correct answer.
  3. 4.4 cm
  4. 13.0 cm

Explanation

The mean is the sum of the readings divided by the number of readings: (4.2 + 4.3 + 4.4) ÷ 3 = 4.3 cm. Averaging reduces the effect of random variation.

Question 13Observing & Measuring

A set of measurements that are all close to each other but far from the true value is:

  1. both accurate and precise
  2. precise but not accurate Correct answer.
  3. neither accurate nor precise at all
  4. accurate but not precise

Explanation

Precision describes how close repeated measurements are to one another, while accuracy describes how close they are to the true value. A tightly clustered set far from the true value is precise but not accurate.

Question 14Observing & Measuring

How many significant figures are in the measurement 0.050 g?

  1. Three
  2. Two Correct answer.
  3. Four
  4. One

Explanation

Leading zeros are never significant, but zeros after the decimal point that follow a non-zero digit are. In 0.050 g the 5 and the final 0 are significant, giving two significant figures.

Question 15Observing & Measuring

Why is a thermometer checked at both the ice point and the steam point?

  1. To test two fixed points Correct answer.
  2. To clean the bulb
  3. To find its mass
  4. To make the liquid move faster

Explanation

Melting ice and boiling water provide two fixed, known temperatures. Checking both tests whether the scale reads correctly at two widely separated points, which reveals a faulty or shifted scale.

Question 16Observing & Measuring

Which is the most reasonable estimate of the mass of a medium apple?

  1. 1500 g
  2. 15 g
  3. 150 g Correct answer.
  4. 15 kg

Explanation

A medium apple has a mass of roughly 100–200 g, so 150 g is the reasonable estimate. 15 g is about the mass of a large coin, while 1500 g and 15 kg are far too heavy.

Question 17Observing & Measuring

A stone is dropped into a measuring cylinder containing 50 mL of water. The water level rises to 68 mL. What is the volume of the stone?

  1. 50 mL
  2. 18 mL Correct answer.
  3. 118 mL
  4. 68 mL

Explanation

The stone displaces its own volume of water, so the rise in level equals the stone's volume: 68 − 50 = 18 mL. The final reading alone still includes the original water.

Question 18Observing & Measuring

A student must measure 25.0 mL of water as precisely as possible. Which instrument is most suitable?

  1. A 100 mL flask
  2. A 50 mL measuring cylinder Correct answer.
  3. A test tube
  4. A 250 mL beaker with coarse marks

Explanation

A measuring cylinder has a graduated scale and a narrow bore, giving smaller reading uncertainty than a beaker, flask or test tube. A cylinder whose capacity is close to the volume also improves precision.

Question 19Observing & Measuring

Why do scientists repeat a measurement several times?

  1. To save time
  2. To reduce random errors Correct answer.
  3. To remove all errors completely
  4. To make the result larger

Explanation

Repeating a measurement and averaging the results reduces the influence of random errors such as small timing or reading variations. It cannot remove systematic errors, which shift every reading in the same direction.

Question 20Observing & Measuring

A length of 2500 mm is equal to:

  1. 2.5 m Correct answer.
  2. 0.25 m
  3. 250 m
  4. 25 m

Explanation

There are 1000 millimetres in a metre, so 2500 mm ÷ 1000 = 2.5 m. Dividing by 100 or 10 gives the wrong unit conversion.

Question 21Observing & Measuring

A measuring cylinder has scale markings every 1 mL. Which value best shows the uncertainty when reading it?

  1. ±0.01 mL
  2. ±2 mL
  3. ±1 mL
  4. ±0.5 mL Correct answer.

Explanation

When the smallest scale division is 1 mL, the reader can usually estimate to about half a division. The uncertainty of a single reading is therefore about ±0.5 mL.

Question 22Observing & Measuring

A spring balance consistently reads 0.5 N too high. How does this affect the results?

  1. The average of many readings removes the shift
  2. Only large readings are affected
  3. Every reading is too high by 0.5 N Correct answer.
  4. Readings scatter randomly about the true value

Explanation

A systematic error affects every reading in the same direction and by the same amount, so averaging does not remove it. Random errors, by contrast, scatter around the true value and tend to cancel when averaged.

Question 23Observing & Measuring

A student measures a length as 9.8 cm. The true length is 10.0 cm. What is the percentage error?

  1. 0.2%
  2. 2% Correct answer.
  3. 98%
  4. 20%

Explanation

Percentage error = (error ÷ true value) × 100 = (0.2 ÷ 10.0) × 100 = 2%. The error is the difference between the measured and true values, not the measured value itself.

Question 24Observing & Measuring

A metal block has a mass of 54.0 g and a volume of 20.0 cm³. What is its density, given to the correct number of significant figures?

  1. 2.70 g/cm³ Correct answer.
  2. 2.7 g/cm³
  3. 1080.0 g/cm³
  4. 0.37 g/cm³

Explanation

Density = mass ÷ volume = 54.0 g ÷ 20.0 cm³ = 2.70 g/cm³. Both measurements have three significant figures, so the answer is also given to three significant figures.

Question 25Observing & Measuring

In an experiment, five readings of a time are 12.1 s, 12.3 s, 12.2 s, 19.8 s and 12.2 s. What is the best action to take?

  1. Repeat the 19.8 s reading Correct answer.
  2. Discard all the readings
  3. Add one second to every reading
  4. Use 19.8 s in the mean

Explanation

The 19.8 s reading is far from the others and is likely an anomaly caused by a timing or recording mistake. The best practice is to repeat that measurement before deciding whether to keep or reject it.

Question 26Observing & Measuring

A ruler is marked with a line every 1 mm. What is the smallest length difference the ruler can show directly from its markings?

  1. 1 mm Correct answer.
  2. 1 cm
  3. 10 mm
  4. 0.1 mm

Explanation

The smallest division on a scale sets the smallest difference that can be read directly from the marks. Changes smaller than one division have to be estimated by eye between the lines.

Question 27Observing & Measuring

A student writes: 'The liquid in the beaker is clear and colourless.' This statement is best described as:

  1. a hypothesis to be tested
  2. a prediction of what will happen
  3. an observation Correct answer.
  4. a conclusion based on the results

Explanation

An observation records what is detected with the senses or simple instruments, without interpretation. Describing a liquid as clear and colourless states only what was seen.

Question 28Observing & Measuring

Which unit is most suitable for recording the volume of a liquid in a laboratory?

  1. litre Correct answer.
  2. gram
  3. newton
  4. second

Explanation

The volume of a liquid is a measure of the space it occupies and is recorded in litres or in millilitres. The other units listed measure force, mass and time.

Question 29Observing & Measuring

A thermometer is marked from −10 °C to 110 °C. What does the −10 °C mark tell you about the thermometer?

  1. the temperature of melting ice
  2. the size of the smallest temperature change it can show
  3. the lowest temperature it can measure Correct answer.
  4. the temperature of boiling water

Explanation

The two end marks of a scale give the range of the instrument. The lower end mark is the coldest temperature the thermometer can read.

Question 30Observing & Measuring

A bottle contains 0.75 L of water. How many millilitres is this?

  1. 0.075 mL
  2. 75 mL
  3. 7500 mL
  4. 750 mL Correct answer.

Explanation

There are 1000 millilitres in one litre, so a volume in litres is converted by multiplying by 1000. Here 0.75 × 1000 = 750.

Question 31Observing & Measuring

A student needs the mass of a 2 g chemical sample to the nearest 0.01 g. Which instrument is most suitable?

  1. a 100 mL measuring cylinder
  2. an electronic balance reading to 0.01 g Correct answer.
  3. a kitchen balance reading to the nearest 1 g
  4. a metre ruler marked in millimetres

Explanation

An instrument can only be read to the smallest step shown on its display or scale. To weigh to the nearest 0.01 g, the balance must show steps of 0.01 g or finer.

Question 32Observing & Measuring

The 0 cm end of a ruler is broken. A student places one end of an object at the 2.0 cm mark and the other end at the 9.5 cm mark. What is the length of the object?

  1. 11.5 cm
  2. 7.5 cm Correct answer.
  3. 5.5 cm
  4. 9.5 cm

Explanation

When the object does not start at the zero mark, its length is the difference between the two scale readings. The starting offset cancels, so 9.5 − 2.0 = 7.5 cm.

Question 33Observing & Measuring

A rectangular block measures 2.0 cm by 3.0 cm by 5.0 cm. What is the volume of the block?

  1. 6 cm³
  2. 30 cm³ Correct answer.
  3. 15 cm³
  4. 10 cm³

Explanation

The volume of a rectangular block is found by multiplying its three dimensions together. Here 2.0 × 3.0 × 5.0 = 30 cm³.

Question 34Observing & Measuring

Which statement describes a random error in a measurement?

  1. All readings are too high by the same amount
  2. The scale divisions are unevenly spaced
  3. Readings scatter about the true value Correct answer.
  4. The balance does not read zero when empty

Explanation

Random errors come from unpredictable variation, so repeated readings fall on both sides of the true value and can be reduced by averaging. The other options describe faults that shift or distort every reading in a fixed way.

Question 35Observing & Measuring

A student times 20 complete swings of a pendulum and divides the total time by 20. Why is this better than timing a single swing?

  1. It reduces the effect of reaction time Correct answer.
  2. It increases the size of the measurement error
  3. It removes the zero error of the stopwatch
  4. It makes the pendulum swing faster

Explanation

Starting and stopping a stopwatch by hand is delayed by reaction time on each occasion. Timing many swings makes this fixed delay a small fraction of the total time, improving the result.

Question 36Observing & Measuring

A spring balance gives the reading 4.5 N for a hanging object. What does this value represent?

  1. the mass in grams
  2. the volume in millilitres
  3. the density in g/cm³
  4. the force in newtons Correct answer.

Explanation

A spring balance measures force by the extension of its spring, and force is recorded in newtons. The reading is the pull of gravity on the object.

Question 37Observing & Measuring

A thermometer is placed in warm water and read straight away. What is the main problem with this?

  1. It has not reached the water temperature Correct answer.
  2. It measures the air temperature instead
  3. The thermometer glass may crack in the warm water
  4. The liquid inside the thermometer will not move

Explanation

A thermometer gives a correct reading only when its bulb has reached the same temperature as the object being measured. Reading immediately gives a value part-way between room temperature and the water temperature.

Question 38Observing & Measuring

A stone is placed in a measuring cylinder and the water level rises from 50 mL to 68 mL. Each reading has an uncertainty of ±1 mL. What is the percentage uncertainty in the volume of the stone?

  1. about 5.6%
  2. about 18%
  3. about 11% Correct answer.
  4. about 2%

Explanation

The volume of the stone is 68 − 50 = 18 mL. When two readings are subtracted, their uncertainties add, so the result is 18 ± 2 mL, giving 2/18 × 100 ≈ 11%.

Question 39Observing & Measuring

A square tile measures 1.2 m by 1.2 m. What is the area of the tile in square centimetres?

  1. 1 440 cm²
  2. 144 cm²
  3. 14 400 cm² Correct answer.
  4. 144 000 cm²

Explanation

Each side is 1.2 m = 120 cm, so the area is 120 × 120 = 14 400 cm². Converting an area from m² to cm² multiplies by 10 000, not by 100.

Question 40Observing & Measuring

A student finds that 10 identical marbles have a total mass of 25.0 g on a balance reading to the nearest 0.1 g. What is the best estimate of the mass of one marble, with its uncertainty?

  1. 2.5 g ± 0.1 g
  2. 2.5 g ± 0.001 g
  3. 2.5 g ± 0.01 g Correct answer.
  4. 0.25 g ± 0.01 g

Explanation

Dividing the total mass by the number of marbles divides the uncertainty by the same number. So 25.0 g ± 0.1 g becomes 2.5 g ± 0.01 g for a single marble.

Question 41Interpreting

A student counts how many bean seeds germinate in four dishes kept at different temperatures. The results are: 5 °C - 3 seeds; 15 °C - 11 seeds; 25 °C - 17 seeds; 35 °C - 6 seeds. At which temperature do most seeds germinate?

  1. 25 °C Correct answer.
  2. 35 °C
  3. 5 °C
  4. 15 °C

Explanation

The greatest number of germinated seeds is 17, and this count was recorded in the dish kept at 25 °C. Comparing the counts directly is the correct way to read a results table.

Question 42Interpreting

A bar chart shows how many students chose each favourite fruit: apples 6, bananas 7, oranges 6, grapes 1. Which two fruits were chosen by equal numbers of students?

  1. Apples and oranges Correct answer.
  2. Bananas and grapes
  3. Apples and bananas
  4. Oranges and grapes

Explanation

The bar for apples and the bar for oranges are the same height, both showing 6 students. Equal bar heights indicate equal counts.

Question 43Interpreting

A cyclist's distance from home is recorded: 0 s - 0 m; 2 s - 20 m; 4 s - 40 m; 6 s - 40 m; 8 s - 60 m. During which time interval is the cyclist's distance from home unchanged?

  1. 0 s and 2 s
  2. 2 s and 4 s
  3. 4 s and 6 s Correct answer.
  4. 6 s and 8 s

Explanation

The distance stays at 40 m between 4 s and 6 s, so the cyclist's position does not change. A flat section on a distance–time graph means no movement.

Question 44Interpreting

A pie chart of a family's daily water use shows: garden one half, laundry one quarter, kitchen one eighth, other one eighth. The family uses 400 L in total. How much water is used for laundry?

  1. 200 L
  2. 25 L
  3. 100 L Correct answer.
  4. 50 L

Explanation

One quarter of 400 L is calculated as 400 ÷ 4, which equals 100 L. The laundry sector is one quarter of the whole pie.

Question 45Interpreting

In a food chain, grass → grasshopper → frog → snake → hawk. A disease kills most of the frogs. What is the most likely immediate effect?

  1. More snakes, more grass
  2. More hawks, fewer grasshoppers
  3. Fewer grasshoppers, more snakes
  4. More grasshoppers, fewer snakes Correct answer.

Explanation

Frogs eat grasshoppers, so fewer frogs means fewer grasshoppers are eaten and their number rises. Snakes eat frogs, so fewer frogs means less food for snakes and their number falls.

Question 46Interpreting

A circuit has one bulb connected to one cell. A second identical cell is added in series, facing the same way. What happens to the bulb?

  1. It goes out
  2. It glows the same
  3. It glows brighter Correct answer.
  4. It glows dimmer

Explanation

Cells in series add their voltages, so the total push on the charges increases. A larger current flows through the bulb, making it glow more brightly.

Question 47Interpreting

A beaker of crushed ice is heated and its temperature recorded every minute. The temperature rises to 0 °C, stays at 0 °C for several minutes, then rises again. What is happening while the temperature stays at 0 °C?

  1. The water is boiling
  2. The ice is cooling down
  3. The water is freezing
  4. The ice is melting Correct answer.

Explanation

At 0 °C, added energy is used to change ice into liquid water rather than to raise the temperature. This constant-temperature stage is the melting point.

Question 48Interpreting

Solubility of a salt in water: 20 °C - 30 g per 100 g water; 40 °C - 40 g; 60 °C - 50 g; 80 °C - 60 g. A student adds 45 g of salt to 100 g of water at 40 °C and stirs. What is seen?

  1. 15 g remains undissolved
  2. 5 g remains undissolved Correct answer.
  3. All 45 g dissolve
  4. No salt dissolves

Explanation

At 40 °C, 100 g of water can dissolve only 40 g of this salt. When 45 g is added, 40 g dissolves and the remaining 5 g stays solid at the bottom.

Question 49Interpreting

A seedling is placed on a windowsill so light comes from one side only. After three days the stem bends towards the window. What does this show?

  1. The stem grows towards the light Correct answer.
  2. The stem grows away from the light
  3. The stem grows towards gravity
  4. The stem grows towards water

Explanation

Bending towards the window shows that the direction of light affects the direction of stem growth. This response is called phototropism.

Question 50Interpreting

A graph shows numbers of hares and lynx over many years. The hare peak occurs about one year before the lynx peak. What do the data suggest?

  1. Lynx rise before hares
  2. Lynx rise after hares Correct answer.
  3. Hares rise after lynx
  4. The two are unrelated

Explanation

The lag between the peaks suggests that lynx numbers increase after hare numbers increase. More hares provide more food, allowing lynx to breed and increase.