AP 8th Physics Textbook Solutions – 3. Particulate Nature of Matter (2026-27)

3 Particulate Nature of Matter

Keep the curiosity alive (Page 110-112)

1. Choose the correct option.

• 1. The primary difference between solids and liquids is that the constituent particles are:
  (i) closely packed in solids, while they are stationary in liquids.

  (ii) far apart in solids and have fixed position in liquids.

  (iii) always moving in solids and have fixed position in liquids.

  (iv) closely packed in solids and move past each other in liquids.
  Answer: (iv) closely packed in solids and move past each other in liquids.

2. Which of the following statements are true? Correct the false statements.

• (i) Melting ice into water is an example of the transformation of a solid into a liquid.
  Answer: True
• (ii) Melting process involves a decrease in interparticle attractions during the transformation.
  Answer: True
• (iii) Solids have a fixed shape and a fixed volume.
  Answer: True
• (iv) The interparticle interactions in solids are very strong, and the interparticle spaces are very small.
  Answer: True
• (v) When we heat camphor in one corner of a room, the fragrance reaches all corners of the room.
  Answer: True
• (vi) On heating, we are adding energy to the camphor, and the energy is released as a smell.
  Answer: False. Correct statement: On heating, we add thermal energy to camphor which increases the movement of its particles, causing them to vaporize and spread through diffusion into the air.

3. Choose the correct answer with justification. If we could remove all the constituent particles from a chair, what would happen?

• (i) Nothing will change.
  (ii) The chair will weigh less due to lost particles.
  (iii) Nothing of the chair will remain.
  Answer: (iii) Nothing of the chair will remain.
  Justification: Matter is entirely composed of its constituent particles. If all particles are removed, no matter remains, so the chair itself will not exist.

4. Why do gases mix easily, while solids do not?

• Gases mix easily because their particles have negligible interparticle attractions and large interparticle spaces, allowing them to move freely and rapidly in all directions. In contrast, particles in solids are tightly packed with very strong interparticle attractions and minimum interparticle space, restricting their movement to only small vibrations about their fixed positions.

5. When spilled on the table, milk in a glass tumbler, flows and spreads out, but the glass tumbler stays in the same shape. Justify this statement.

• Milk is a liquid, so its particles are free to move within a limited space, giving it a definite volume but no fixed shape; hence it flows and spreads when spilled. The glass tumbler is a solid, meaning its particles are tightly held in fixed positions by strong interparticle attractions, giving it a definite shape and volume that does not change.

6. Represent diagrammatically the changes in the arrangement of particles as ice melts and transforms into water vapour.

• As ice (solid) melts into water (liquid), the particles gain thermal energy, vibrations increase, interparticle forces weaken slightly, and particles move slightly further apart to form a liquid arrangement. Upon further heating to boiling point, the particles gain enough energy to overcome attractive forces entirely, transforming into water vapour (gas) where particles are widely separated and move freely in all available space.

7. Draw a picture representing particles present in the following:

• (i) Aluminium foil
  (ii) Glycerin
  (iii) Methane gas
  Answer:
  (i) Aluminium foil (Solid): Particles represented as closely packed spheres in a fixed, regular pattern with minimum interparticle space.
  (ii) Glycerin (Liquid): Particles represented as slightly less closely packed spheres with small spaces between them, showing a fluid arrangement.
  (iii) Methane gas (Gas): Particles represented as widely separated, independent spheres with maximum interparticle spacing and random positions.

8. Observe Fig. 3.16a which shows the image of a candle that was just extinguished after burning for some time. Identify the different states of wax in the figure and match them with Fig. 3.16b showing the arrangement of particles.

• - Solid wax (solid body of the candle): Matches with the solid particle arrangement (tightly packed regular grid).
  - Melted liquid wax (near the wick): Matches with the liquid particle arrangement (closely packed but slightly loose and irregular).
  - Wax vapour / smoke (rising from the wick): Matches with the gaseous particle arrangement (few particles far apart with maximum spacing).

9. Why does the water in the ocean taste salty, even though the salt is not visible? Explain.

• Salt consists of tiny constituent particles. When salt dissolves in ocean water, it breaks down into these constituent particles, which are far too small to be seen with the naked eye or even through an ordinary microscope. These particles occupy the interparticle spaces between water molecules and spread uniformly throughout the water, which is why the water tastes salty even though the solid salt is invisible.

10. Grains of rice and rice flour take the shape of the container when placed in different jars. Are they solids or liquids? Explain.

• Grains of rice and rice flour are solids. Although they take the shape of the container they are poured into due to the gaps between individual solid pieces or fine particles, each individual grain or speck retains its own fixed shape, size, and volume, which is a characteristic property of solids.

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