MP Board 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 occupies space and has mass.
Examples: Air and water.

2. List the characteristics of particles of matter.
Answer: Particles are extremely tiny, have spaces between them, are always in motion, and attract each other.

3. Why do solids have a fixed shape but gases do not?
Answer: Solid particles are tightly packed with strong forces; gas particles are loosely packed and move freely.

4. Explain why gases are highly compressible but solids are not.
Answer: Gases have large spaces between particles allowing compression; solids have no such spaces.

5. Differentiate diffusion in liquids and gases.
Answer: Diffusion in gases is faster due to higher speed of particles; in liquids it’s slower because of stronger attraction.

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

• Solids have fixed shape and volume and are incompressible.

• Liquids have fixed volume but no fixed shape and are slightly compressible.

• Gases have no fixed shape or volume and are highly compressible.

7. What effect does temperature have on particle motion?
Answer: Increasing temperature increases kinetic energy, making particles move faster.

8. What is the boiling point of water? What happens at this point?
Answer: 100 °C; water changes into steam while temperature remains constant.

9. Why does temperature remain constant during melting of ice?
Answer: Heat is used to break molecular bonds (latent heat), not to increase temperature.

10. Define sublimation and name two examples.
Answer: Sublimation is direct solid-to-gas transition.
Examples: Camphor, ammonium chloride.

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

12. Define latent heat of vaporisation with example.
Answer: Heat required to convert 1 kg of liquid into gas at boiling point without temperature change.
Example: Converting water to steam at 100 °C.

13. Why do wet clothes dry faster on a windy day?
Answer: Wind removes water vapor quickly, increasing evaporation rate.

14. What is evaporation? Name four factors affecting it.
Answer: Evaporation is liquid turning into vapor below its boiling point.
Factors: Surface area, temperature, wind speed, humidity.

15. Why is water in earthen pots cooler than in plastic bottles?
Answer: Water seeps through pores and evaporates, cooling the water.

16. Why do we feel cool under a fan after sweating?
Answer: Air movement accelerates sweat evaporation, absorbing heat from the body.

17. Define condensation and give one example.
Answer: Condensation is gas turning into liquid.
Example: Water droplets on a cold bottle.

18. Explain why gases have more kinetic energy than solids.
Answer: Gas particles move faster and more freely due to weak intermolecular forces.

19. What is the interconversion of states of matter?
Answer: Conversion of matter from one state to another by changing temperature or pressure.

20. State two conditions for gas liquefaction.
Answer: Lowering temperature and increasing pressure.

21. Give one difference between evaporation and boiling.
Answer: Boiling occurs at a fixed temperature; evaporation can occur at any temperature.

22. Define ‘fluid.’ Which states are fluids?
Answer: Fluids can flow; liquids and gases are fluids.

23. Why are naphthalene balls used in clothes without leaving liquid?
Answer: They sublimate from solid to gas directly, leaving no liquid.

24. Why does camphor disappear in rituals?
Answer: Camphor sublimes, producing a fragrant gas and symbolizing purity.

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

• Melting: Ice in drinks.

• Boiling: Cooking.

• Sublimation: Mothball use.

• Condensation: Dew formation.

• Evaporation: Drying clothes.