Chemistry · Unit 3

States of Matter

Solids, liquids, gases and changes

Solid, liquid and gas are three arrangements of the same particles at different energies, and every change between them is energy going in or coming out.

The unit covers the three states and their particle arrangements, the phase changes connecting them, and plasma - the fourth state, which is rare on Earth and is most of the visible matter in the universe.

This unit breaks down into 16 short steps and 95 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: 16
Questions: 95
Difficulty: 1-3

What this unit covers

Phase Change
Plasma
Liquid
Gas
Solid

Where this fits

Follows Atoms. Gases and Gas Laws takes the gas state much further.

Where people slip

Temperature does not rise during a change of state. Energy going into melting ice breaks bonds rather than raising the temperature, which is why iced water sits at zero until the last ice has gone.

How the unit is structured

States of Matter runs as 16 short steps that unlock in order. 12 are practice rounds and 4 are challenge rounds that pull together everything before them. Questions start at difficulty 1 and climb to 3 as you progress.

Step 1 · easierStep 16 · 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 95 in the unit altogether.

Gas

Fact or fibLevel 1
1. A gas will spread out to fill any container it is placed in.
Answer: True
Gas particles move freely and spread to fill all the available space.
Fill the blankLevel 1
2. The spreading of particles from where they are crowded to where they are spread out is called ____.
- diffusioncorrect
- condensation
- freezing
- deposition
Diffusion is the movement of particles from a region of higher concentration to a region of lower concentration.
Odd one outLevel 1
3. Which one is the odd one out?
- Oxygencorrect
- Iron
- Copper
- Gold
Iron, copper and gold are solids at room temperature, while oxygen is a gas.
Type the answerLevel 1
4. Dry ice is the solid form of which gas? Type the gas name.
Answer: carbon dioxide
Dry ice is solid carbon dioxide, which sublimes straight back into carbon dioxide gas.
Multiple choiceLevel 2
5. How do the particles in a gas behave compared with those in a solid?
- They move quickly and are far apartcorrect
- They stay locked in a rigid grid
- They pack tightly and only vibrate
- They stop moving entirely
Gas particles have lots of energy, moving fast and spread far apart.
True or falseLevel 2
6. Unlike solids and liquids, a gas can easily be squeezed into a much smaller volume.
Answer: True
Because gas particles have large gaps between them, gases are easily compressed, unlike solids and liquids.
Put in orderLevel 3
7. Arrange these noble gases in order of increasing boiling point.
Answer: Helium -> Neon -> Argon -> Krypton
London dispersion forces strengthen as the number of electrons rises, so boiling point increases down the group from helium to krypton.

Liquid

Multiple choiceLevel 1
8. A liquid has a fixed volume but takes the shape of what?
- Its containercorrect
- Nothing, it keeps its own shape
- The nearest solid
- The whole room
Liquids keep a fixed volume but flow to take the shape of their container.
Choose all that applyLevel 2
9. Which of these would make a puddle of water evaporate faster? Select all that apply.
- A higher temperaturecorrect
- A windier daycorrect
- A larger surface areacorrect
- A cooler, still day
Higher temperature, more wind and a larger surface area all speed up evaporation.
Fact or fibLevel 2
10. The vapour pressure of a liquid rises as its temperature increases.
Answer: True
Higher temperature gives more molecules enough energy to escape the surface, so vapour pressure increases with temperature.
Fill the blankLevel 2
11. A liquid with a high vapour pressure evaporates easily and is described as highly ____.
- volatilecorrect
- viscous
- dense
- saturated
Volatile liquids have high vapour pressures at a given temperature and evaporate readily, such as petrol or ethanol.
True or falseLevel 2
12. Liquids are difficult to compress because their particles are already close together.
Answer: True
Liquid particles are packed nearly as tightly as in solids, so liquids barely compress.
Type the answerLevel 2
13. Polar molecules such as HCl attract one another through permanent dipole-____ forces. Type the missing word.
Answer: dipole
Permanent dipole-dipole forces act between molecules that have a permanent separation of charge, like HCl.
Match the pairsLevel 3
14. Match each substance to the strongest intermolecular (or interparticle) force acting between its particles.
Answer: CH4 = London forces only; HCl = Permanent dipole-dipole; NH3 = Hydrogen bonding; NaCl = Ionic attraction
CH4 has only London forces, HCl adds permanent dipole-dipole, NH3 can hydrogen bond, and NaCl is held by ionic attractions.

Phase Change

Fill the blankLevel 1
15. When a solid turns into a liquid, the process is called ____.
- Meltingcorrect
- Freezing
- Boiling
- Condensation
Adding heat to a solid until it becomes liquid is called melting.
Multiple choiceLevel 1
16. What is the general name for a liquid changing into a gas?
- Evaporationcorrect
- Condensation
- Freezing
- Melting
When a liquid turns into a gas it evaporates, or boils if it happens rapidly.
Build the sentenceLevel 2
17. Arrange the words to describe how clouds begin to form.
Answer: water vapour condenses into tiny droplets
As water vapour cools, it condenses into tiny droplets that gather to form clouds.
Guess the numberLevel 2
18. At sea level, at what temperature in Celsius does water boil?
Answer: 100 °C
Pure water boils at 100 degrees Celsius at standard sea-level pressure.
Match the pairsLevel 2
19. Match each change of state to an everyday example.
Answer: Melting = Ice cube turning to water; Freezing = Water turning to ice; Condensation = Water droplets forming on a cold glass; Evaporation = A puddle drying in the sun
Melting, freezing, condensation and evaporation each describe matter moving between the solid, liquid and gas states.
Odd one outLevel 2
20. Which of these is the odd one out?
- Dissolvingcorrect
- Melting
- Freezing
- Boiling
Melting, freezing and boiling are changes of state, but dissolving is a mixing process, not a change of state.

Plasma

Multiple choiceLevel 1
21. Plasma, the fourth state of matter, is basically what?
- A superheated, ionized gas
- A very cold solid
- A thick liquid
- A type of metal
Plasma forms when a gas gets so hot that its atoms lose electrons and become ionized, as inside stars.
Multiple choiceLevel 1
22. Which of these is an everyday example of plasma?
- A bolt of lightningcorrect
- An ice cube
- A glass of water
- A balloon full of air
Lightning is plasma, a very hot state in which gas particles have been ionised.
Tap the pairsLevel 2
23. Tap to match each state of matter to an everyday example of it.
Answer: Solid = A block of ice; Liquid = Milk in a glass; Gas = Helium in a balloon; Plasma = The glowing gas in a neon sign
Ice is a solid, milk is a liquid, helium is a gas, and the glow inside a neon sign is plasma.
Multiple choiceLevel 3
24. Which state of matter is the most common in the entire universe?
- Plasmacorrect
- Solid
- Liquid
- Gas
Most visible matter in the universe is plasma, because stars are made of it.

Solid

Build the sentenceLevel 2
25. Build the sentence explaining why metals conduct electricity.
Answer: metals conduct electricity because of delocalised electrons
Metals conduct because their delocalised outer electrons are free to move and carry charge through the lattice.
Choose all that applyLevel 2
26. Which statements about crystalline solids are correct? Select all that apply.
- Their particles form a regular repeating latticecorrect
- They have long-range ordercorrect
- They melt at a sharp, definite temperature
- They have no fixed shape or volume
Crystalline solids have a regular, repeating long-range ordered lattice and a sharp melting point; a lack of definite shape describes fluids, not crystals.
Fact or fibLevel 2
27. Because ice is less dense than the liquid water around it, ice floats.
Answer: True
Being less dense, ice displaces enough water to float, which is why lakes freeze from the top down.
Fill the blankLevel 3
28. Cubic close packing repeats layers in an ABC ABC pattern, while hexagonal close packing repeats them in an ____ pattern.
- ABABcorrect
- ABCD
- AABB
- ACAC
Hexagonal close packing stacks layers as ABAB, whereas cubic close packing (face-centred cubic) uses an ABC repeat.
Guess the numberLevel 3
29. In a close-packed metal (hexagonal or cubic close packing), how many nearest neighbours does each atom touch?
Answer: 12 neighbours
Both hexagonal and cubic close-packed structures give a coordination number of 12, the maximum for equal spheres.
Match the pairsLevel 3
30. Match each crystal type to one of its characteristic physical properties.
Answer: Ionic = Conducts when molten but not when solid; Giant covalent = Very high melting point and usually an insulator; Molecular = Soft with a low melting point; Metallic = Malleable and conducts electricity when solid
Ionic solids conduct only when molten or dissolved, giant covalent solids melt very high, molecular solids are soft and low melting, and metals are malleable conductors.

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 17 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
Listen and choose
Match the pairs
Multiple choice
Odd one out
Picture question
Put in order
Sequence recall
Sort into groups
Spell it
Tap the pairs
True or false
Type the answer

Practise States of Matter

95 questions across 16 steps. Start with step one and crawl at your own pace.

Play this unit

Read about States of Matter

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

How Crystallisation Purifies a SolidCrystallisation separates a dissolved solid from a solution by changing how much solute the solvent can hold. Careful heating, cooling and filtration can produce crystals while leaving many impurities behind.August 8, 2026 · 5 min read

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