Science · Unit 5

Solids, Liquids and Gases

States of matter and everyday changes

The three states are usually taught as three boxes, which hides the interesting part. What matters is the arrangement and energy of the particles, and every change of state is a change in those two things.

The unit covers melting, freezing, evaporation and condensation, the difference between a change you can undo and one you cannot, and what happens when things dissolve rather than melt.

This unit breaks down into 21 short steps and 127 questions, starting at difficulty 1 and building to 3. Below you can see exactly what it covers, how the path is structured, and worked examples with explanations.

Steps: 21
Questions: 127
Difficulty: 1-3

What this unit covers

Melting and Freezing
The Three States
Reversible and Irreversible Changes
Mixing and Dissolving
Evaporating and Condensing

Where this fits

Follows Everyday Materials. Chemistry's States of Matter is the same content with the particle model made explicit.

Where people slip

Dissolving is not melting. Sugar in tea has not melted - it has spread out among the water particles, and evaporating the water brings it back.

How the unit is structured

Solids, Liquids and Gases runs as 21 short steps that unlock in order. 15 are practice rounds and 6 are challenge rounds that pull together everything before them. Questions start at difficulty 1 and climb to 3 as you progress.

Step 1 · easierStep 21 · harder

Challenge rounds

Example questions

30 real questions from this unit, with the answer and the reason behind it, grouped by what they practise. There are 127 in the unit altogether.

Evaporating and Condensing

Fill the blankLevel 1
1. Condensation is when a gas cools down and turns back into a ____.
- liquidcorrect
- solid
- gas
- cloud
When water vapor cools, it condenses into tiny drops of liquid water.
Multiple choiceLevel 1
2. What happens to a puddle of water on a warm, sunny day?
- It slowly evaporates into the aircorrect
- It freezes into ice
- It turns into a solid
- It gets deeper
The sun's heat turns the puddle water into water vapor, a gas that spreads into the air.
Choose all that applyLevel 2
3. Which of these help wet clothes dry faster? Pick all that apply.
- Warm sunshinecorrect
- A breeze of moving aircorrect
- Spreading the clothes out widecorrect
- Putting them in a cold, closed box
Heat, moving air, and more surface area all make water evaporate more quickly.
Guess the numberLevel 2
4. At about what temperature in degrees C does water boil and turn into steam?
Answer: 100 degrees C
Water boils at about 100 degrees C, quickly turning into steam, which is water in gas form.
Match the pairsLevel 2
5. Match each everyday scene to what happens to the water.
Answer: Wet towel on a warm line = Dries as water evaporates; Cold can of soda = Gets water drops on the outside; Bathroom mirror after a hot shower = Fogs up with tiny droplets; Boiling kettle = Sends steam into the air
Evaporation turns liquid water into vapour, and condensation turns vapour back into liquid drops.
Fact or fibLevel 3
6. Evaporation can only happen when water reaches its boiling point.
Answer: False
Evaporation happens from a liquid's surface at many temperatures, which is why puddles dry up without boiling.

Melting and Freezing

Fill the blankLevel 1
7. When a liquid gets cold enough it freezes and turns into a ____.
- solidcorrect
- gas
- liquid
- cloud
Freezing removes heat from a liquid until it becomes a solid, like water turning into ice.
Multiple choiceLevel 1
8. What do we call the change when liquid water turns into solid ice?
- Freezingcorrect
- Melting
- Boiling
- Dissolving
Freezing is when a liquid cools down and becomes a solid, such as water becoming ice.
Fact or fibLevel 2
9. A metal spoon needs much more heat to melt than a lump of butter does.
Answer: True
Different solids melt at different temperatures, and metal has a much higher melting point than butter.
Guess the numberLevel 2
10. At what temperature in degrees C does water freeze into ice?
Answer: 0 degrees C
Pure water freezes at 0 degrees C, the point where liquid water turns into solid ice.
Match the pairsLevel 2
11. Match each change to its opposite change.
Answer: Melting = Freezing; Heating up = Cooling down; Solid to liquid = Liquid to solid; Adding heat = Taking heat away
Melting and freezing are opposites: one adds heat while the other takes heat away.
Choose all that applyLevel 3
12. Which of these will MELT if you heat them enough? Pick all that apply.
- Chocolatecorrect
- Candle waxcorrect
- Buttercorrect
- A wooden spoon
Chocolate, wax, and butter melt when heated, but wood burns and chars instead of melting.

Mixing and Dissolving

Build the sentenceLevel 2
13. Build a true sentence about dissolving sugar.
Answer: Stirring helps sugar dissolve faster
Stirring spreads the sugar through the water, so it dissolves faster.
Choose all that applyLevel 2
14. Which of these make sugar dissolve faster in water? Pick all that apply.
- Stirring the watercorrect
- Using warmer watercorrect
- Crushing the sugar into smaller grainscorrect
- Using ice-cold water
Stirring, warmth, and smaller grains all speed up how fast the sugar dissolves.
Fact or fibLevel 2
15. You can get the salt back from salt water by letting the water evaporate away.
Answer: True
When the water evaporates, it leaves the solid salt behind, so dissolving salt can be undone.
Fill the blankLevel 2
16. When a solid dissolves completely in a liquid, the even mixture it makes is called a ____.
- solutioncorrect
- puddle
- powder
- shadow
A solution is the smooth, even mixture made when a solid fully dissolves in a liquid.
Match the pairsLevel 2
17. Match each solid to what happens when you stir it into water.
Answer: Sugar = Dissolves and seems to disappear; Sand = Sinks to the bottom; Salt = Dissolves into a clear solution; Cooking oil = Floats on top of the water
Some solids dissolve into the water while others sink or float instead.
Multiple choiceLevel 2
18. You stir sugar into water until you can no longer see it. What happened to the sugar?
- It dissolved and spread all through the watercorrect
- It disappeared and no longer exists
- It sank to the bottom in one lump
- It turned into a gas
Dissolved sugar is still there, spread evenly through the water, which is why the water tastes sweet.

Reversible and Irreversible Changes

Build the sentenceLevel 2
19. Build a sentence about dissolving sugar.
Answer: Dissolving sugar in water is a reversible change
Dissolving is reversible because evaporating the water leaves the sugar behind again.
Choose all that applyLevel 2
20. Which of these changes are irreversible? Pick all that apply.
- Burning papercorrect
- Baking a cakecorrect
- Cooking an eggcorrect
- Melting butter
Burning paper, baking a cake, and cooking an egg cannot be undone, but melted butter can be frozen again.
Fact or fibLevel 2
21. When you mix vinegar and baking soda, they fizz and make a new gas, and this change cannot be undone.
Answer: True
The fizzing makes a brand-new gas, so it is an irreversible change.
Fill the blankLevel 2
22. A change that makes a new material and cannot be undone is called an ____ change.
- irreversiblecorrect
- reversible
- melting
- frozen
Irreversible changes, like burning or cooking, make new materials and cannot be reversed.
Multiple choiceLevel 2
23. Which of these changes can be reversed?
- Melting an ice cubecorrect
- Frying an egg
- Baking a loaf of bread
- Toasting a slice of bread
Melted ice can be frozen again, but frying, baking, and toasting make new materials that cannot go back.
Picture questionLevel 2
24. 🎂 Baking turns runny batter into this cake for good. What type of change is baking a cake?
- Irreversible - a new material formscorrect
- Reversible - you can turn it back into batter
- Just melting
- Just freezing
Baking makes new substances, so a cake cannot be turned back into batter.

The Three States

Build the sentenceLevel 2
25. Build a sentence describing how gas particles behave.
Answer: Gas particles move fast and spread out
Gas particles have lots of energy, so they move fast and spread out to fill space.
Choose all that applyLevel 2
26. Which of these are solids? Pick all that apply.
- A rockcorrect
- A wooden blockcorrect
- An ice cubecorrect
- Orange juice
Rocks, wood, and ice all keep a fixed shape, so they are solids, while orange juice is a liquid.
Fact or fibLevel 2
27. A solid keeps the same amount, or volume, even when you move it to a different container.
Answer: True
A solid stays the same size and shape, so its volume does not change in a new container.
Fill the blankLevel 2
28. A gas has no fixed shape and spreads out to fill ____ of the space it is in.
- allcorrect
- none
- half
- the top
A gas spreads out in every direction until it fills all of its container.
Guess the numberLevel 2
29. A fizzy drink with ice cubes has solid ice, liquid drink, and gas bubbles. How many states of matter is that?
Answer: 3 states
Ice is a solid, the drink is a liquid, and the bubbles are a gas, which makes three states in one glass.
Match the pairsLevel 3
30. Match each state of matter to how its particles move.
Answer: Solid = Vibrate in fixed positions; Liquid = Slide and roll past each other; Gas = Zoom quickly in all directions
Particles move more freely as matter changes from solid to liquid to gas.

Where these questions come from. Each unit starts as a plan of the concepts it should cover and the difficulty it should span. Questions are written against that plan with AI assistance, then checked by a validator that rejects anything without a single defensible answer, an explanation, or plausible wrong options. How we write questions sets out the whole process, and corrections are fixed in the bank and reach the site and the app the same day.

How you practise

This unit mixes 14 different question formats, so you are recalling and applying rather than recognising the same layout every time.

Build the sentence
Choose all that apply
Fact or fib
Fill the blank
Guess the number
Match the pairs
Multiple choice
Odd one out
Picture question
Put in order
Sort into groups
Spell it
True or false
Type the answer

Practise Solids, Liquids and Gases

127 questions across 21 steps. Start with step one and crawl at your own pace.

Play this unit

Read about Solids, Liquids and Gases

Explainers from our blog on what this unit covers. Each one ends with real questions from the bank.

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