O Level / IGCSE Chemistry chapter 1: States of matter MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
44 exam-style questions on States of matter, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. Oxygen, O2, and carbon dioxide, CO2, are at the same temperature. Which statement is correct?
A
CO2 molecules move faster on average, because each contains more atoms
B
both move at the same average speed, because they are at the same temperature
C
the molecules have the same average kinetic energy, but O2 molecules move faster because they are lighter
D
O2 molecules have more kinetic energy, which is why they diffuse faster
Show answer
Answer: C. Temperature fixes the average kinetic energy, not the speed. With equal energy, the lighter O2 (Mr 32) moves faster than CO2 (Mr 44) and diffuses faster.
2. A balloon is moved from a warm room into a cold freezer. The pressure outside stays the same. What happens to the balloon, and why?
A
it shrinks, because the gas particles move more slowly and hit the inside of the balloon less often and less hard
B
it shrinks, because the gas particles themselves become smaller
C
it gets bigger, because cold gas particles spread further apart
D
it stays the same size, because the number of particles inside does not change
Show answer
Answer: A. Slower particles exert less pressure on the inside, so the balloon contracts until the pressures balance again. The particles do not change size.
3. Which change of state happens only at the surface of a liquid and can take place at temperatures below the boiling point?
A
boiling
B
condensing
C
evaporating
D
freezing
Show answer
Answer: C. In evaporation the more energetic particles at the surface escape at any temperature. Boiling happens throughout the liquid, and only at the boiling point.
4. A drop of food colouring is added, without stirring, to beaker A of water at 20 °C and beaker B of water at 60 °C. What is observed and why?
A
the colour spreads faster in A, because cold water is denser and pushes the dye along
B
the colour spreads at the same rate in both, because the dye particles are the same
C
the colour spreads faster in B, because the dye particles become smaller when hot
D
the colour spreads faster in B, because the particles have more kinetic energy and move faster
Show answer
Answer: D. At a higher temperature particles move faster, so diffusion is faster. Particles do not change size when heated.
5. A gas jar of bromine vapour is joined to a gas jar containing a vacuum. The brown colour fills the empty jar almost at once, but takes many minutes to fill a jar of air. Why?
A
bromine particles move faster in a vacuum because they have more kinetic energy there
B
the vacuum pulls the bromine particles in by attraction
C
with no air particles to collide with, the bromine particles travel straight across without being slowed down
D
air particles react with bromine and stop it moving
Show answer
Answer: C. In air the bromine particles keep colliding with air particles and change direction, so spreading is slow. In a vacuum there is nothing to collide with. A vacuum does not "pull", and the temperature (so the energy) is the same.
6. Why can a solid not be compressed noticeably?
A
its particles are already very close together with almost no space between them
B
its particles do not move at all
C
its particles are themselves very hard
D
its particles repel each other strongly however far apart they are
Show answer
Answer: A. In a solid the particles are packed closely together, so there is almost no empty space to squeeze out. The particles still vibrate, so "do not move at all" is wrong.
7. A beaker of water is left in a warm room and slowly evaporates. Why does the water that remains become slightly cooler?
A
evaporation only happens at the boiling point, so the cooling must come from the room
B
the remaining particles become heavier and slower as they clump together
C
particles from the air enter the water and take energy from it as they dissolve
D
the fastest particles escape, so the average kinetic energy of the particles left falls
Show answer
Answer: D. Only the fastest particles at the surface have enough energy to escape. Losing them lowers the average kinetic energy, and so the temperature, of the liquid left behind.
8. A porous pot containing air is sealed except for a tube leading to a pressure gauge. A beaker of hydrogen is placed over the pot. The pressure inside the pot rises at first. Why?
A
hydrogen molecules diffuse into the pot faster than the heavier nitrogen and oxygen molecules diffuse out
B
nitrogen and oxygen molecules diffuse out faster than hydrogen diffuses in
C
hydrogen reacts with oxygen inside the pot to form more gas
D
hydrogen molecules are larger than air molecules, so they push the air together
Show answer
Answer: A. H2 (Mr 2) diffuses much faster than N2 (28) or O2 (32), so more particles enter the pot than leave it and the pressure rises.
9. A pure liquid is cooled from 90 °C to 10 °C. Its temperature falls to 62 °C, stays at 62 °C for 5 minutes, then falls again. What is the state of the substance at 30 °C, and what is 62 °C?
A
liquid; 62 °C is its boiling point
B
solid; 62 °C is its melting point
C
gas; 62 °C is its boiling point
D
liquid; 62 °C is its melting point
Show answer
Answer: B. The substance starts as a liquid, so the flat section is freezing, and the freezing point equals the melting point. Below 62 °C it is a solid.
10. A drop of bromine is placed at the bottom of a gas jar of air. After some time the brown colour fills the jar. What is this process called?
A
evaporation
B
diffusion
C
condensation
D
sublimation
Show answer
Answer: B. Bromine vapour particles move randomly and spread out from where they are concentrated to where they are not: diffusion.
44, each with the answer and a short explanation, across 2 topics: Solids, liquids and gases, Diffusion. Every chapter test draws ten of them, so you can take it many times.
Is the O Level / IGCSE Chemistry chapter 1 test free?
Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.
How is the chapter test marked?
The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.
