NCERT Solutions for Class 8 Science Curiosity Chapter 7 Particulate Nature of Matter

1. Choose the correct option.
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.
See AnswerThe correct choice is (iv) closely packed in solids and move past each other in liquids. Think of it like this: in a solid, the particles are like students sitting in fixed desks in a classroom—they can fidget (vibrate), but they stay in one spot. In a liquid, the particles are like students during a break in the classroom—they are still close together but can walk around and slide past one another.

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.
(ii) Melting process involves a decrease in interparticle attractions during the transformation.
(iii) Solids have a fixed shape and a fixed volume.
(iv) The interparticle interactions in solids are very strong, and the interparticle spaces are very small.
(v) When we heat camphor in one corner of a room, the fragrance reaches all corners of the room.
(vi) On heating, we are adding energy to the camphor and the energy is released as a smell.
See Answer(i) True. This is the classic definition of melting.
(ii) True. The heat energy supplied during melting gives the particles enough power to weaken the forces holding them in fixed positions, allowing them to start moving more freely.
(iii) True. These are the two defining properties of a solid.
(iv) True. This is why solids are rigid and generally dense. The strong attractions and tight packing keep everything in place.
(v) True. The heat causes the solid camphor to turn into a gas, and these gas particles then spread throughout the room.
(vi) False. This statement is a bit mixed up! The correction is: On heating, we are adding energy to the camphor, which causes its particles to change into a gas. These gas particles then spread out and mix with the air and when they reach our nose, we detect them as a smell. The energy causes the change, it isn’t released as a smell.

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.
See AnswerThe correct answer is (iii) Nothing of the chair will remain. A chair, like all matter, is made up entirely of its constituent particles. It isn’t a container “for” particles; it “is” the particles arranged in a specific way. If you were to magically remove every single particle, you would be removing the very substance of the chair and absolutely nothing would be left behind.

4. Why do gases mix easily, while solids do not?
See AnswerThis is all about freedom of movement! In gases, the particles are very far apart, have extremely weak forces of attraction between them, and are zipping around randomly at high speeds. This allows them to move freely and intermingle easily with the particles of other gases. In solids, the particles are locked into a tight, rigid structure by strong forces. They can only vibrate in their fixed positions and cannot move from place to place, so they can’t mix with other solids on their own.

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.
See AnswerThis observation illustrates the difference between liquids and solids.
The milk is a liquid. Its particles are held together by forces that are strong enough to keep them close but weak enough to let them slide past one another. This ability to slide is why the milk flows and takes the shape of the surface it’s on.
The glass tumbler is a solid. Its particles are bound by very strong forces into a fixed, rigid structure. The particles can’t move from their positions, which is why the tumbler maintains its definite shape and doesn’t flow.

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

7. Draw a picture representing particles present in the following:
(i) Aluminium foil
Answer:

(ii) Glycerin
Answer:

(iii) Methane gas
Answer:

8. Observe Fig. 7.16a 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. 7.16b showing the arrangement of particles.
See AnswerSolid wax: This is the main body of the candle. Its particle arrangement would match the diagram of tightly packed, ordered particles.
Liquid wax: This is the small pool of melted wax at the base of the wick. Its particle arrangement would match the diagram of closely packed but disordered particles.
Gaseous wax: This is the trail of smoke or vapour rising from the hot wick. Its particle arrangement would match the diagram of particles that are very far apart and moving randomly.

9. Why does the water in the ocean taste salty, even though the salt is not visible? Explain.
See AnswerThe salt in the ocean has dissolved in the water. This means the salt crystals have broken down into their individual constituent particles (ions), which are incredibly tiny—far too small to be seen with the naked eye. These invisible salt particles spread out and mix completely with the water particles, occupying the spaces between them. So, even though you can’t see the salt, its particles are evenly distributed throughout the water, which is why every drop tastes salty.

10. Grains of rice and rice flour take the shape of the container when placed in different jars. Are they solids or liquids? Explain.
See AnswerGrains of rice and rice flour are definitely solids. While a large quantity of them can be poured and will take the shape of the container, this is a property of a collection of many small solids, not a property of a liquid. The key difference is that each individual grain of rice or speck of flour is a solid with its own fixed shape and volume. A true liquid flows because its fundamental constituent particles (molecules) are sliding past one another. In the case of rice, it’s the large grains sliding past each other, not the particles that make up the rice itself.