Matter in Our Surroundings – Short Answer Type Questions
CBSE Class 9 • Chemistry
Chapter 1: Matter in Our Surroundings — 50 Short Answer Type Questions & Answers (NCERT-aligned)
Topic-wise structure for guided revision and board exam practice.
50 Short Q&A
Exam-friendly • Printable • Use as revision or classroom handout
CBSE Board Exam — How to use this page
1. Read definitions (5–7 min)
2. Practice short answers (20–30 min)
3. Convert to long answers for writing practice
Answer each question in 3–5 sentences for short-answer practice. Diagrams where requested earn extra marks — include if time permits.
Basics — What is Matter? (Q1–Q6)
- 1. Define matter.
Matter is anything that has mass and occupies space (i.e., has volume). All physical objects and substances around us are forms of matter.
- 2. State two fundamental properties of matter.
The two fundamental properties are: (1) matter occupies space (has volume) and (2) matter has mass.
- 3. Is light matter? Explain briefly.
No. Light does not occupy space in the usual sense and has no rest mass, so it is not classified as matter; rather it is energy in the form of electromagnetic radiation.
- 4. Name the three common states of matter and give one example for each.
Solid (e.g., iron), Liquid (e.g., water), Gas (e.g., oxygen).
- 5. What is meant by the term 'state of matter'?
A 'state of matter' refers to the distinct forms in which matter can exist — primarily solid, liquid and gas — characterized by particle arrangement and energy.
- 6. Give a simple experiment to show that matter occupies space.
Place a small rock in a measuring cylinder partly filled with water and observe the rise in water level; the rise shows the rock occupies space (displaces water).
Properties of Solids, Liquids & Gases (Q7–Q16)
- 7. Why do solids have a fixed shape?
Particles in solids are tightly packed in a fixed, ordered arrangement and can only vibrate about fixed positions; strong interparticle forces hold them in place, giving solids a definite shape.
- 8. Explain why liquids take the shape of their container but have a definite volume.
Liquid particles are close but not fixed; they can move/slide past each other, allowing the liquid to flow and take the container's shape, while interparticle attraction maintains a definite volume.
- 9. Why are gases easily compressible?
Gas particles are widely separated with large voids between them; under pressure particles can be pushed closer, reducing volume — hence gases are easily compressible.
- 10. Compare interparticle forces in solids, liquids and gases.
Interparticle forces are strongest in solids (keep fixed positions), weaker in liquids (allow limited movement), and weakest or negligible in gases (particles move freely).
- 11. Give two real-life examples that show liquid flow.
Pouring water from a jug and oil flowing through a pipeline both show liquids flow due to particles sliding past one another.
- 12. What characteristic of gas particles explains diffusion?
High kinetic energy and large separation allow gas particles to move randomly and spread out, causing diffusion to occur rapidly in gases.
- 13. Can a substance change state without a change in its chemical composition? Explain with an example.
Yes. A physical change of state (e.g., ice melting to water) changes only the arrangement and energy of particles, not chemical identity; ice and water are both H₂O.
- 14. Why is diffusion slower in liquids than in gases?
Particles in liquids are closer and experience greater friction and attractions than in gases, so their random motion is slower, making diffusion slower in liquids.
- 15. Explain with a diagram the arrangement of particles in solids, liquids and gases.
(Answer guideline) Draw three boxes labeled solid/liquid/gas showing: solid — tightly packed ordered dots; liquid — closely packed but disordered dots with small gaps; gas — widely spaced dots. Label 'fixed positions', 'slide past each other', 'free movement' respectively.
- 16. State one practical consequence of the difference in compressibility between liquids and gases.
Hydraulic systems rely on liquid incompressibility to transmit force; in contrast, compressibility of air is used in pneumatic systems to absorb shocks.
Change of State (Q17–Q26)
- 17. Define melting point and give an example.
Melting point is the temperature at which a solid turns into liquid at atmospheric pressure; e.g., ice melts at 0°C (at 1 atm).
- 18. Distinguish between evaporation and boiling.
Evaporation occurs at the liquid surface at any temperature and causes cooling; boiling is a bulk phenomenon occurring at a specific temperature where vapour bubbles form throughout the liquid (boiling point).
- 19. Explain why evaporation causes cooling.
During evaporation higher-energy molecules escape from the liquid's surface, reducing the average kinetic energy of remaining molecules and thus lowering temperature (cooling effect).
- 20. What is condensation? Provide an example.
Condensation is the change of vapour (gas) into liquid, often on cooling or pressure increase; e.g., water droplets forming on a cold glass.
- 21. Define sublimation and name two substances that sublime.
Sublimation is the direct transition between solid and gas without passing through liquid; camphor and dry ice (solid CO₂) are common examples.
- 22. Why does water boil at lower temperature on a mountain?
At higher altitudes atmospheric pressure is lower, so vapour pressure equals external pressure at a lower temperature, lowering the boiling point of water.
- 23. How does humidity affect the rate of evaporation?
High humidity means air already contains water vapour so the vapour pressure gradient is reduced, slowing evaporation; low humidity increases evaporation rate.
- 24. Describe an activity to show evaporation is a surface phenomenon.
Place equal amounts of water in two shallow dishes (different surface areas). The dish with larger surface area will dry faster, demonstrating evaporation occurs at the surface.
- 25. Explain why steam at 100°C can be more dangerous than boiling water at 100°C.
Steam contains more latent heat (heat of vaporization) than boiling water; when steam condenses on skin it releases this latent heat, causing more severe burns.
- 26. What is meant by 'latent heat' in boiling?
Latent heat is the energy absorbed or released during a change of state (like boiling) without a temperature change; during boiling, energy goes into changing state rather than raising temperature.
Particle Nature of Matter (Q27–Q34)
- 27. State the basic postulates of particle theory of matter.
Matter consists of very small particles (atoms/molecules) in constant motion; there are forces of attraction between them; higher temperature increases particle motion (kinetic energy).
- 28. How does kinetic theory explain pressure of a gas?
Gas pressure arises from collisions of moving gas particles with container walls; more frequent and forceful collisions (higher speed/temperature) produce greater pressure.
- 29. Why does increasing temperature increase diffusion rate?
Higher temperature increases particle kinetic energy and speed, causing faster random motion and quicker mixing (higher diffusion rate).
- 30. Does the size of molecules change on heating? Explain.
No. Heating changes particle motion/kinetic energy and average separation, not the intrinsic size of atoms or molecules.
- 31. Explain how particle arrangement differs in solid and liquid using particle model.
In solids particles are arranged in a regular, closely packed structure; in liquids particles are close but arranged randomly with freedom to move/slide around each other.
- 32. Give an example where particle theory helps explain a real-life observation.
Diffusion of perfume in a room: particles of perfume move randomly and spread, demonstrating particle motion and mixing without bulk movement.
- 33. How would you explain thermal expansion using particle model?
When heated, particles vibrate faster and average separation increases, leading to expansion of the substance; this is thermal expansion.
- 34. What experimental evidence supports the particle nature of matter?
Brownian motion — random motion of pollen particles in water seen under a microscope — and diffusion experiments provide direct evidence of tiny moving particles.
Diffusion & Brownian Motion (Q35–Q39)
- 35. Define diffusion and give an example.
Diffusion is the spontaneous mixing of particles due to their random motion; example: dye spreading in water or perfume scent spreading in a room.
- 36. What is Brownian motion and who discovered it?
Brownian motion is the erratic movement of microscopic particles suspended in fluid due to collisions with molecules; observed by botanist Robert Brown in 1827.
- 37. How does Brownian motion support kinetic theory?
Brownian motion shows visible particles being constantly jostled by unseen molecules, providing visual evidence of molecular motion and existence.
- 38. Why is diffusion visible in gases quickly but not in solids?
Gas particles move freely and rapidly with large separations, enabling quick mixing; in solids particles are tightly bound so diffusion is extremely slow and often negligible.
- 39. Suggest a classroom demonstration to show diffusion in liquids.
Add a drop of potassium permanganate or dye to still water and observe slow spreading of color; this shows diffusion without stirring.
Evaporation, Boiling & Applications (Q40–Q44)
- 40. List four factors that affect the rate of evaporation.
Temperature (higher increases), surface area (larger increases), humidity (lower increases), and wind/surface movement (increases).
- 41. Explain why sweating cools the body.
Sweat evaporates from the skin surface; higher-energy molecules escape, lowering average kinetic energy of remaining molecules and thus cooling the skin/body.
- 42. What is meant by 'boiling point' of a liquid?
Boiling point is the temperature at which the vapour pressure of the liquid equals external pressure, causing vapour bubbles to form inside the liquid and rise to the surface.
- 43. Why does salt lower the freezing point of water (practical application)?
Salt dissolves into ions, disrupting water's ability to form an ordered solid lattice, requiring lower temperature to freeze — used to de-ice roads by lowering freezing point.
- 44. Give one safety precaution when handling boiling liquids in the lab.
Use tongs or protective gloves, keep face and hands away from steam, and use a lid or safety shield to avoid splashes and steam burns.
Forces, Compressibility & Thermal Expansion (Q45–Q48)
- 45. Explain compressibility in terms of particle arrangement.
Compressibility depends on available space between particles: gases have large interparticle spaces allowing compression; liquids and solids have little free space and are much less compressible.
- 46. Why are solids generally incompressible?
Because particles are tightly packed and in fixed positions, making it difficult to further decrease the volume by applying pressure.
- 47. Give an example of thermal expansion used in everyday devices.
Bimetallic strips in thermostats (used in electric irons and temperature control devices) bend with temperature changes due to different expansion rates of two metals.
- 48. How is the concept of compressibility used in hydraulic systems?
Hydraulic systems use incompressible liquids to transmit force efficiently — pressure applied at one point is transmitted undiminished to perform work elsewhere.
Physical vs Chemical Change & Revision (Q49–Q50)
- 49. Distinguish between physical and chemical change with examples.
Physical change alters state or appearance only (e.g., ice melting to water), while chemical change forms new substances with different properties (e.g., iron rusting to form iron oxide).
- 50. How can students use these short answers effectively for board exam preparation?
Use these answers to build speed and accuracy: practise writing concise definitions, add a labelled diagram where helpful, and expand 1–2 answers into longer explanations weekly for deeper understanding.
Tips: Convert these short answers into flashcards; draw simple labelled diagrams for states of matter; practice 3 timed write-ups of any one short answer per day to improve writing speed.
Prepared strictly as per NCERT syllabus — ideal for CBSE Class 9 board exam standard.
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