🧪 Chemistry · Topic 10 of 10
Start with the study notes on Matter: Elements, Compounds & Mixtures (definitions, examples and a quick revision), then work through 60 practice questions, each with the correct answer and a clear explanation of why it is right. When you are ready, take this topic as an interactive quiz to test yourself.
Topic overview
Matter is anything that has mass and takes up space.
Examples:
Matter is made of tiny particles that:
Example: Sugar dissolved in a full glass of water does not make it overflow: the sugar particles fit into the spaces between the water particles.
Space between particles: Solid < Liquid < Gas
Example: Gases can be compressed a lot, which is why LPG and CNG can be packed into cylinders.
Diffusion is the spreading out and mixing of particles on their own, because they are always moving. It is fastest in gases, slower in liquids and very slow in solids, and it speeds up when it is warmer.
Examples:
Remember: While ice melts, its temperature stays at 0 °C. The heat supplied goes into separating the particles, not warming them. This hidden heat is called latent heat.
Evaporation is a liquid turning into vapour at its surface, at any temperature. It cools what is left behind.
Examples:
An element is a pure substance made of only one kind of atom. It cannot be broken into anything simpler.
Example: Oxygen, gold, iron, copper and carbon.
About 118 elements are known. They are grouped as metals, non-metals and metalloids.
A compound is a pure substance formed when two or more elements combine chemically in a fixed ratio. Its properties are completely different from those of its elements, and it can be separated only by chemical methods.
Examples:
A mixture contains two or more substances mixed physically, in any proportion. Each part keeps its own properties, and the parts can be separated by physical methods.
Examples:
Matter → Pure substances (elements, compounds) + Mixtures (homogeneous, heterogeneous)
Example: Distilled water is a pure substance; sea water and milk are mixtures.
| Misconception | Correct understanding |
|---|---|
| Air is a compound of gases. | Air is a mixture: its parts vary and can be separated physically. |
| A compound behaves like the elements in it. | A compound's properties are completely different; salt is nothing like sodium or chlorine. |
| Evaporation happens only at 100 °C. | Evaporation happens at any temperature; boiling happens at 100 °C. |
| Heat added to melting ice raises its temperature. | The temperature stays at 0 °C until all the ice has melted (latent heat). |
| Brass is a compound. | Brass is an alloy, which is a homogeneous mixture. |
Which state of matter has a fixed volume but no fixed shape?
A liquid.
Why can gases be compressed easily?
There is a lot of space between their particles.
Why does the smell of cooking food spread through the house?
Its particles diffuse through the air.
Why does water stay cool in an earthen pot?
Water seeping through the pores evaporates and takes heat away.
Is water an element, a compound or a mixture?
A compound of hydrogen and oxygen (H₂O).
Is air an element, a compound or a mixture?
A mixture.
What is the chemical symbol for iron?
Fe (from its Latin name, ferrum).
Give one example each of a solution and a suspension.
Sugar in water (solution); chalk in water (suspension).
Key takeaway: Everything is made of tiny moving particles. Every sample of matter is either a pure substance (an element or a compound) or a mixture.
Notes written by Velnov for Class 6–8 students, following the topics of the NCERT science syllabus.
Q1. easy
Anything that has mass and occupies space is called:
Answer: A — Matter
Everything around us - a book, water, air, a stone - is matter, because it has mass and takes up space (volume). Light and heat are energy, not matter.
Q2. easy
The three common states of matter are:
Answer: A — Solid, liquid and gas
Matter exists mainly as solids, liquids and gases. Plasma is a fourth state found in stars and lightning.
Q3. medium
Which state of matter has a DEFINITE shape and a definite volume?
Answer: A — Solid
In a solid, particles are tightly packed in fixed positions, so a solid keeps both its shape and its volume.
Q4. medium
Which state of matter has a definite VOLUME but no definite shape?
Answer: A — Liquid
A liquid takes the shape of its container but keeps the same volume, because its particles can slide past each other while staying close together.
Q5. medium
Which state of matter has NEITHER a definite shape NOR a definite volume?
Answer: A — Gas
Gas particles are far apart and move freely, so a gas spreads out to fill whatever container it is in, taking both its shape and volume.
Q8. medium
The spreading out of a substance on its own, like the smell of perfume filling a room, is called:
Answer: A — Diffusion
Diffusion is the intermixing of particles due to their constant random motion. It is fastest in gases, slower in liquids and extremely slow in solids.
Q10. medium
Diffusion becomes FASTER when the temperature is:
Answer: A — Increased
Higher temperature gives particles more kinetic energy, so they move faster and mix more quickly. Sugar dissolves faster in hot tea than in cold water for the same reason.
Q12. medium
Which of these is an ELEMENT?
Answer: A — Copper
Copper is made of only copper atoms. Water and salt are compounds made of two or more elements, and air is a mixture.
Q14. medium
Which of these is a COMPOUND?
Answer: A — Water (H2O)
Water is formed when hydrogen and oxygen combine chemically in a 2:1 ratio. Oxygen is an element, and air and brass are mixtures.
Q16. medium
Which of these is a MIXTURE?
Answer: A — Air
Air is a mixture of nitrogen, oxygen, argon, carbon dioxide and water vapour in varying proportions. The other three are compounds.
Q18. medium
A mixture of iron filings and sulphur powder is a mixture, but heating them forms iron sulphide, which is:
Answer: A — A compound with completely different properties
In the mixture, a magnet still attracts the iron. After heating, the black iron sulphide formed is not attracted by a magnet - a new substance with new properties.
Q20. medium
A mixture in which the different components can be SEEN separately is called:
Answer: A — A heterogeneous mixture
Sand and water, oil and water, and a mixture of pulses are heterogeneous - the parts are visibly distinct and unevenly distributed.
Q22. medium
In a salt solution, the SOLUTE is:
Answer: A — The salt (the substance that dissolves)
The solute is the substance that dissolves, and the solvent is the one that does the dissolving. Salt is the solute; water is the solvent.
Q23. medium
Water is called the UNIVERSAL SOLVENT because it:
Answer: A — Dissolves a very large number of substances
Water dissolves more substances than any other liquid, which is why it carries nutrients in our bodies and in plants. It still cannot dissolve oil, wax or sand.
Q25. medium
Milk is an example of:
Answer: A — A colloid
Milk is a colloid - tiny fat droplets are dispersed in water. The particles are bigger than in a solution but too small to settle, so milk looks uniform but is cloudy.
Q27. medium
The smallest particle of an element that can take part in a chemical reaction is called:
Answer: A — An atom
Atoms are the basic building blocks of matter. They combine to form molecules and compounds.
Q29. medium
The chemical formula of water, H2O, tells us that one molecule of water contains:
Answer: A — Two hydrogen atoms and one oxygen atom
The subscript shows the number of atoms of each element. H2O means 2 hydrogen atoms bonded to 1 oxygen atom - always in that fixed ratio.
Q31. medium
The chemical symbol for IRON is:
Answer: A — Fe
Iron's symbol Fe comes from its Latin name ferrum. Ir is iridium and I is iodine.
Q33. medium
The chemical formula of carbon dioxide is:
Answer: A — CO2
Carbon dioxide has one carbon atom bonded to two oxygen atoms. CO is carbon monoxide, a very different and poisonous gas.
Q35. medium
The change from solid to liquid on heating is called:
Answer: A — Melting
At the melting point, the particles gain enough energy to break free from their fixed positions and begin sliding over each other, turning the solid into a liquid.
Q36. medium
The change from liquid to solid on cooling is called:
Answer: A — Freezing (solidification)
As a liquid cools, its particles lose energy and settle into fixed positions, forming a solid. Water freezes into ice at 0 °C.
Q38. medium
Evaporation differs from boiling because evaporation:
Answer: A — Takes place only at the surface and at any temperature
Evaporation is a surface phenomenon that occurs at all temperatures, which is why wet clothes dry even in the shade. Boiling occurs throughout the liquid at a fixed temperature.
Q40. medium
Water in an earthen pot (matka) stays cool because:
Answer: A — Water seeps through the tiny pores and evaporates, taking heat from the pot
The porous clay lets a little water reach the outer surface, where it evaporates. The evaporation draws heat from the remaining water, keeping it cool.
Q42. medium
Clothes dry faster on a windy day because wind:
Answer: A — Carries away the water vapour, allowing more evaporation
Moving air removes the humid layer just above the wet cloth and replaces it with drier air, so evaporation can continue rapidly.
Q44. medium
When sugar dissolves in a full glass of water, the water does NOT overflow because:
Answer: A — Sugar particles fit into the spaces between water particles
There are gaps between water particles, and the much smaller dissolved sugar particles occupy them - direct evidence that matter is particulate with spaces in between.
Q46. medium
Alloys such as brass and steel are classified as:
Answer: A — Homogeneous mixtures (solid solutions)
Alloys are uniform throughout and have no fixed composition ratio, so they are homogeneous mixtures - specifically, solid solutions of metals.
Q48. medium
Elements are broadly classified into:
Answer: A — Metals, non-metals and metalloids
Metals are lustrous conductors, non-metals are mostly dull insulators, and metalloids such as silicon show properties of both.
Q50. medium
The components of a compound can be separated only by:
Answer: A — Chemical methods
Because the elements in a compound are chemically bonded, physical methods cannot separate them. Electrolysis or heating with a suitable reagent is needed.
Q52. medium
Which of these shows that air is a MIXTURE and not a compound?
Answer: A — Its components are present in varying proportions and can be separated physically
The proportion of gases in air varies from place to place, no chemical reaction happens when they mix, and fractional distillation of liquid air separates them physically.
Q54. medium
Dry ice is solid carbon dioxide. It is called 'dry' because it:
Answer: A — Sublimes directly into gas without becoming a liquid
Unlike ordinary ice, dry ice leaves no puddle - it turns straight into carbon dioxide gas, which is why it is used to keep things frozen and to create stage fog.
Q56. medium
During melting, the temperature of ice stays at 0 °C even though heat is being supplied because:
Answer: A — The heat is used to break the forces holding the particles in fixed positions (latent heat)
The energy supplied during a change of state goes into overcoming the attraction between particles rather than raising their speed, so the temperature stays constant. This is latent heat.
Q58. medium
Which of these is the correct classification of MATTER?
Answer: A — Matter → pure substances (elements, compounds) and mixtures (homogeneous, heterogeneous)
Matter divides first into pure substances and mixtures. Pure substances are elements or compounds; mixtures are homogeneous (solutions) or heterogeneous (suspensions and others).
Q60. medium
Why can you smell food cooking in the kitchen from another room?
Answer: A — Vapour particles from the food diffuse through the air and reach your nose
Particles of the aromatic substances leave the hot food, mix with the constantly moving air particles and spread through the house by diffusion - everyday evidence that matter is made of moving particles.
Q6. hard
Gases can be compressed easily because:
Answer: A — The spaces between gas particles are very large
Large gaps between particles allow them to be pushed closer together. This is why LPG and CNG can be compressed into cylinders, while liquids and solids cannot.
Q7. hard
The force of attraction between particles is STRONGEST in:
Answer: A — Solids
Solids have the strongest interparticle forces, which hold the particles in fixed positions. The forces are weaker in liquids and almost negligible in gases.
Q9. hard
Diffusion is FASTEST in gases because gas particles:
Answer: A — Move very fast and have large spaces between them
With high speeds and plenty of empty space, gas particles spread through one another quickly. In solids, fixed particles allow almost no diffusion.
Q11. hard
A pure substance made up of only ONE kind of atom is called:
Answer: A — An element
Elements such as oxygen, gold, iron and carbon cannot be broken down into simpler substances by any chemical process.
Q13. hard
A pure substance formed when two or more elements combine CHEMICALLY in a fixed ratio is called:
Answer: A — A compound
In a compound, the elements are chemically bonded in a definite proportion, and the compound's properties are quite different from those of its constituent elements.
Q15. hard
A substance made of two or more substances mixed physically, in any proportion, is called:
Answer: A — A mixture
In a mixture the components keep their own properties and can be present in any ratio. They can usually be separated by physical methods.
Q17. hard
Which statement correctly distinguishes a compound from a mixture?
Answer: A — A compound has a fixed composition and new properties; a mixture has variable composition and keeps its components' properties
Making a compound is a chemical change with heat or light often given out, and the product behaves nothing like its elements. Making a mixture is just physical mixing.
Q19. hard
A mixture that is UNIFORM throughout, with the same composition everywhere, is called:
Answer: A — A homogeneous mixture
Salt solution, sugar solution, air and alloys are homogeneous - you cannot see separate parts, and every sample has the same composition.
Q21. hard
A homogeneous mixture of a solute dissolved in a solvent is called:
Answer: A — A solution
In a solution, the solute particles are so small that they cannot be seen or filtered out, and the mixture is transparent and uniform - like salt in water.
Q24. hard
A mixture in which solid particles are visible and settle down on standing is called:
Answer: A — A suspension
In a suspension, such as chalk powder in water or muddy water, the particles are large enough to be seen, to scatter light and to settle out. They can be filtered.
Q26. hard
Which of these can be separated by FILTRATION?
Answer: A — A suspension of chalk in water
Filtration removes particles that are undissolved. Suspensions can be filtered; true solutions cannot, because the dissolved particles pass through the filter paper.
Q28. hard
A group of two or more atoms chemically bonded together is called:
Answer: A — A molecule
A molecule may contain atoms of the same element (O2, N2) or of different elements (H2O, CO2). It is the smallest unit of a substance that can exist independently.
Q30. hard
The chemical symbol for SODIUM is:
Answer: A — Na
Some symbols come from Latin names: sodium is Na (natrium), potassium is K (kalium), iron is Fe (ferrum) and gold is Au (aurum).
Q32. hard
The chemical symbol for GOLD is:
Answer: A — Au
Gold is Au, from the Latin aurum. Ag is silver (argentum) and Gd is gadolinium.
Q34. hard
The chemical formula of common salt is:
Answer: A — NaCl
Sodium chloride, NaCl, is common table salt. NaOH is caustic soda, Na2CO3 is washing soda and NaHCO3 is baking soda.
Q37. hard
The temperature at which a liquid changes into vapour throughout its bulk is called its:
Answer: A — Boiling point
At the boiling point, vapour bubbles form throughout the liquid, not just at the surface. Water boils at 100 °C at normal atmospheric pressure.
Q39. hard
Evaporation causes COOLING because:
Answer: A — The escaping particles take heat energy away from the liquid and its surroundings
Only the most energetic particles escape, and they draw the latent heat needed from what is left behind. This is why sweating cools us and why water stays cool in an earthen pot.
Q41. hard
Which factor does NOT increase the rate of evaporation?
Answer: A — Increasing the humidity of the air
Humid air already holds a lot of water vapour, so it accepts less, slowing evaporation. Heat, a larger surface and moving air all speed it up.
Q43. hard
Matter is made up of tiny particles that:
Answer: A — Have spaces between them and are in constant motion
These are the key ideas of the particle theory of matter. Constant motion explains diffusion, and the spaces between particles explain dissolving and compressibility.
Q45. hard
Which of these is a pure substance?
Answer: A — Distilled water
Distilled water contains only water molecules, so it is pure. Sea water, milk and air are all mixtures containing several different substances.
Q47. hard
How many elements are known at present (approximately)?
Answer: A — About 118
About 118 elements are known, of which roughly 92 occur naturally. The rest have been made artificially in laboratories.
Q49. hard
Which of these correctly describes the properties of a compound compared with its elements?
Answer: A — The compound's properties are entirely different from those of the elements it contains
Sodium is a violently reactive metal and chlorine a poisonous gas, yet sodium chloride is edible table salt. Chemical combination creates entirely new properties.
Q51. hard
The process of splitting water into hydrogen and oxygen using electricity is called:
Answer: A — Electrolysis
Electrolysis passes an electric current through water, decomposing it into hydrogen at the negative electrode and oxygen at the positive one, in a 2:1 volume ratio.
Q53. hard
Sublimation is the change of state from:
Answer: A — Solid directly to gas, without passing through the liquid state
Camphor, naphthalene, ammonium chloride, iodine and dry ice sublime. The reverse change, gas to solid, is called deposition.
Q55. hard
The temperature at which a solid melts and the temperature at which the liquid freezes are:
Answer: A — The same for a given substance
Melting point and freezing point are the same temperature approached from opposite directions. For water, both are 0 °C at normal pressure.
Q57. hard
Which sequence correctly shows increasing separation between particles?
Answer: A — Solid < Liquid < Gas
Particles are closest in solids, slightly further apart in liquids, and very widely spaced in gases. This explains their densities, compressibility and rates of diffusion.
Q59. hard
Which overall statement about matter is CORRECT?
Answer: A — Matter is made of tiny moving particles, exists as solid, liquid or gas, and is classified into elements, compounds and mixtures
This sums up the topic: the particle nature of matter explains states, diffusion, dissolving and changes of state; and every sample of matter is either a pure substance (element or compound) or a mixture.