NCERT Solutions Class 9 Science Chapter 1 – Matter in Our Surroundings

Matter in Our Surroundings – Important Questions with Answers

1. Define matter. Give two examples.
Answer: Matter is anything that has mass and occupies space. Examples: air and water.

2. State the characteristics of particles of matter.
Answer:

• Particles are very small.

• They have spaces between them.

• They are in constant motion.

• They attract each other.

3. Why do solids have a fixed shape but gases do not?
Answer: Solids have tightly packed particles with strong intermolecular forces, while gases have loosely packed particles that move freely.

4. Give reasons: Gases are highly compressible but solids are not.
Answer: Gas particles have large spaces between them, allowing compression. Solid particles are closely packed, leaving no space for compression.

5. Differentiate between diffusion in liquids and gases.
Answer:

• Diffusion is faster in gases due to high particle speed.

• It is slower in liquids due to stronger intermolecular forces.

6. List any three differences between solids, liquids, and gases.
Answer:

7. What is the effect of temperature on the motion of particles?
Answer: An increase in temperature increases the kinetic energy of particles, making them move faster.

8. What is the boiling point of water? What happens at this point?
Answer: The boiling point of water is 100°C. At this point, water changes into steam (gas) without a rise in temperature.

9. Why does the temperature remain constant during the melting of ice?
Answer: The heat supplied is used to break the bonds between ice molecules (latent heat of fusion), not to raise temperature.

10. Define the term sublimation. Name two sublimating substances.
Answer: Sublimation is the process where a solid changes directly to gas without becoming liquid. Examples: camphor and ammonium chloride.

11. Explain why a gas fills the entire volume of the container.
Answer: Gas particles move freely in all directions due to weak intermolecular forces and occupy all available space.

12. Define latent heat of vaporisation with an example.
Answer: The amount of heat required to convert 1 kg of a liquid into gas without changing its temperature. Example: boiling water into steam.

13. Why do wet clothes dry faster on a windy day?
Answer: Wind increases the rate of evaporation by removing the water vapour from the surface quickly.

14. What is evaporation? List four factors affecting it.
Answer:
Evaporation is the process of liquid changing into vapour at temperatures below its boiling point.
Factors:

1. Surface area

2. Temperature

3. Wind speed

4. Humidity

15. Why is water stored in earthen pots cooler than in plastic bottles?
Answer: Water seeps through the pores and evaporates from the pot’s surface, taking heat from the water and cooling it.

16. Why do we feel cool when we sit under a fan after sweating?
Answer: The fan increases evaporation of sweat, which absorbs heat from our body, causing a cooling effect.

17. Define condensation and give one real-life example.
Answer: Condensation is the process of gas changing into liquid. Example: Water droplets on the outside of a cold bottle.

18. Explain with reasons: Gases have more kinetic energy than solids.
Answer: Gas particles move more freely and rapidly due to weaker intermolecular forces, giving them higher kinetic energy.

19. What is meant by the interconversion of states of matter?
Answer: It is the process of changing matter from one state to another (e.g., solid to liquid) by changing temperature or pressure.

20. State the two conditions under which a gas can be liquefied.
Answer:

1. Increasing pressure

2. Lowering temperature

21. Write one difference between evaporation and boiling.
Answer:

• Boiling: Happens at a fixed temperature (boiling point).

• Evaporation: Can occur at any temperature.

22. What is meant by the term ‘fluid’? Which states of matter are fluids?
Answer: Fluids are substances that can flow. Liquids and gases are both fluids.

23. Why are naphthalene balls stored in clothes without leaving a liquid trace?
Answer: Because naphthalene undergoes sublimation, changing directly from solid to gas without becoming liquid.

24. Why is camphor used in religious rituals even though it disappears over time?
Answer: Camphor sublimes, releasing a fragrant gas, and its disappearing nature symbolizes purity and devotion.

25. Give one practical application of each: melting, boiling, sublimation, condensation, and evaporation.
Answer:

• Melting: Ice turning into water in drinks

• Boiling: Cooking food with boiling water

• Sublimation: Storing clothes with naphthalene balls

• Condensation: Formation of dew drops

• Evaporation: Drying clothes under the sun