Particulate Nature of Matter — Mastery

Q1. The chapter opens with the question: 'Why can stones or sand be piled up, but not a liquid like water?' The simplest reason from the chapter is that

• A. Stones and sand have fixed shape (solid); water has no fixed shape (liquid) and flows
• B. Stones are alive and arrange themselves; water has no will
• C. Sand is invisible underwater and so water cannot be piled
• D. Water is heavier than sand and so it sinks instead of piling

Q2. The opener asks: we cannot see air, yet it adds weight to an inflated balloon. The chapter's explanation is that

• A. Balloons are made of a special heavy rubber that gains weight on stretching
• B. Air has mass and volume because it is matter, made of constituent particles
• C. Air is a magnetic substance attracted by Earth's core
• D. Sound waves from outside add their weight to the air inside

Q3. The chapter asks students to imagine that the grinding of chalk continues without stopping. At what stage does this imaginary process end?

• A. When the chalk becomes a liquid
• B. When chalk powder turns black in colour
• C. When the chalk particles cannot be broken down any further
• D. Grinding can never come to an end — it goes on for ever

Q4. About the constituent particles of matter, the chapter states that

• A. They are easily visible with the naked eye
• B. They are visible only with a magnifying glass
• C. They are visible with an ordinary classroom microscope
• D. They are so small that they cannot be seen even through an ordinary microscope

Q5. The 'A step further' box at the end of the chapter introduces the names of constituent particles. According to it

• A. All matter is made of just one type of particle called the iota
• B. The tiny particles that make up all matter are atoms and molecules
• C. Matter is made of grains, pebbles and dust only
• D. Matter is made of electric currents only

Q6. The 'Our scientific heritage' box names an ancient Indian philosopher who first wrote about the idea of tiny indivisible particles called Parmanu. He is

• A. Aryabhata, in the Aryabhatiya
• B. Charaka, in the Charaka Samhita
• C. Acharya Kanad, in the Vaisheshika Sutras
• D. Bhaskara, in the Lilavati

Q7. Activity 7.3 asks students to collect a few solid objects and observe their shapes and sizes. Which of the following sets is taken in the activity?

• A. Iron nail, rock salt, stone, wood, key, piece of aluminium
• B. Milk, sugar, salt water, ice cube, vapour
• C. Balloon air, kerosene, lemon juice, smoke
• D. Sand, water, oil, kerosene, copper wire

Q8. Ravi pushes his finger through water in a shallow vessel and removes it. He notices the water surface restores. This shows that

• A. Water particles are stationary like solid particles
• B. Interparticle attractions in water are slightly weaker than in solids but still strong enough to keep particles close together
• C. Water has no interparticle attractions at all
• D. Pushing a finger destroys water particles temporarily

Q9. The bubbles seen rising through boiling water indicate that

• A. Vapour is forming only at the surface of the water
• B. Vapour is forming both inside the liquid and at the surface
• C. Water is changing into ice inside the pan
• D. Air is being absorbed from the room into the water

Q10. A small amount of cooking gas leaks in a closed kitchen of a Patna flat. Within minutes its smell can be sensed in every corner of the kitchen. Which property of gases best explains this?

• A. Gases have a fixed shape that matches the kitchen
• B. Gas particles move freely in all directions and occupy the entire available space
• C. Gases solidify at low room temperatures and float as dust
• D. Gases sink to the floor instantly and stay there

Q11. After Activity 7.6, when Sara stops pushing the plunger inside the syringe, the plunger springs back to its original position. Why?

• A. The thumb pulls the plunger back chemically
• B. The compressed gas particles spread out again into the larger interparticle space available
• C. The syringe wall becomes magnetic and repels the plunger
• D. The plunger is heated by friction and expands

Q12. A Class 8 student tells Madam Asha that the gaps between solid particles must be filled with air. Which response is the most effective for correcting this misconception?

• A. Tell the student the answer is wrong and move on
• B. Show Fig. 7.12 of the three states and read the chapter line that says the spaces between solid particles contain nothing at all, since air is itself made of constituent particles
• C. Punish the student for not paying attention
• D. Skip the topic and revise it later in higher classes

Q13. A teacher wants Class 8 students to compare the compressibility of air and water using Activity 7.6. Which is the most appropriate teaching sequence?

• A. Tell the students the answer in advance, then push the plunger themselves while students watch
• B. Ask students to predict what will happen with air and with water, then push the plunger themselves, then ask students to explain the difference using interparticle spacing
• C. Skip the activity and read the conclusion aloud from the textbook
• D. Ask students to read silently and write the answer in their notebooks

Q14. Exercise 7 asks students to draw the particle picture for three substances. Which match between substance and state is correct?

• A. Aluminium foil — gas; Glycerin — solid; Methane gas — liquid
• B. Aluminium foil — solid (particles closely packed); Glycerin — liquid (particles slightly farther apart); Methane gas — gas (particles freely moving)
• C. All three are gases because their packets contain air
• D. All three are liquids because each can flow

Q15. Exercise 9 asks: why does ocean water taste salty even though the salt is not visible? The best explanation, using the chapter's ideas, is

• A. Salt particles have dissolved in water — they have broken into constituent particles and occupy interparticle spaces between water particles, so we cannot see them but we can taste them
• B. There is no salt in ocean water; only the salty smell of fish makes it taste salty
• C. Salt has chemically turned into water; nothing of salt remains
• D. Salt is too heavy and has settled at the ocean floor only

Q16. The opener notes that water poured into folded hands takes their shape, but loses that shape on being released. Considering the chapter: I. This shows that water has no fixed shape. II. This shows that water has a fixed shape but no fixed volume. III. This shows that water particles can move freely within a limited space. Which are correct?

• A. I and II only
• B. II and III only
• C. I and III only
• D. All three

Q17. About a single tiny grain of sugar, the chapter says that

• A. It is the smallest possible unit of sugar; nothing inside it
• B. It is itself one constituent particle of sugar
• C. It is a chemical mixture of sugar and water
• D. It is made up of millions and millions of constituent particles

Q18. About interparticle attractions, consider the statements: I. Their strength depends on the nature of the substance and the interparticle distance. II. A slight increase in distance decreases the attractive force drastically. III. The strength of these forces ultimately decides the physical state of the substance. Which are correct as per the chapter?

• A. I and II only
• B. II and III only
• C. I and III only
• D. All three

Q19. Assertion (A): In a solid, particles cannot move past one another and exchange positions. Reason (R): Interparticle attractions in a solid are very strong, holding particles in fixed positions.

• A. Both A and R are true, and R is the correct explanation of A
• B. Both A and R are true, but R is NOT the correct explanation of A
• C. A is true, R is false
• D. A is false, R is true

Q20. About interparticle attractions in liquids compared to solids, the chapter says they are

• A. Much stronger than in solids
• B. Negligible, like in gases
• C. Equal to those in gases
• D. Slightly weaker than in solids but still strong enough to keep particles close together

Q21. Consider the following about gases: I. The interparticle attractions in gases are negligible. II. Gas particles move freely in all directions. III. Gases do not have a fixed shape or a fixed volume. Which are correct?

• A. I and II only
• B. II and III only
• C. I and III only
• D. All three

Q22. A cyclist pumps air into a bicycle tyre. Inside the pump, the volume of air decreases as the cyclist pushes the handle. Which property of gases, established in Activity 7.6, is being used?

• A. Gases have a fixed shape that resists the handle
• B. Liquid water inside the pump prevents compression
• C. Solid air particles slip past one another smoothly
• D. Gas particles have large interparticle spaces that reduce under external pressure

Q23. Fig. 7.12 in the chapter shows magnified schematic pictures of interparticle spacing in three states of matter. Which order of spacing (smallest to largest) does it convey?

• A. Liquid < Solid < Gas
• B. Gas < Solid < Liquid
• C. Gas < Liquid < Solid
• D. Solid < Liquid < Gas

Q24. Assertion (A): Potassium permanganate spreads fastest in hot water and slowest in ice-cold water. Reason (R): The movement of water particles increases when heat is provided.

• A. Both A and R are true, and R is the correct explanation of A
• B. Both A and R are true, but R is NOT the correct explanation of A
• C. A is true, R is false
• D. A is false, R is true

Q25. The chapter's 'wrap up' explains that the physical state of matter is decided by

• A. The colour of the particles
• B. Whether the substance is alive or non-living
• C. The number of constituent particles in one gram
• D. The thermal (heat) energy of the particles, which determines interparticle distance and hence attractive force

Q26. Exercise 2 (vi) records the wrong statement: 'On heating, we are adding energy to the camphor, and the energy is released as a smell.' How should a teacher correct this for a Class 8 student?

• A. Tell the student the answer is unimportant and skip it
• B. Mark it correct, since heating camphor does cause a smell
• C. Explain that on heating, camphor particles gain thermal energy and escape into the gaseous state; the 'smell' is the camphor particles themselves reaching our nose, not 'energy released as smell'
• D. Tell the student that the smell is actually heat radiated from the camphor

Q27. Exercise 8 shows a candle that was just extinguished (Fig. 7.16a) and asks students to identify the states of wax visible. Which set is correct?

• A. Only the solid wax of the candle body
• B. Only the liquid wax forming around the wick
• C. Only the wax vapour rising as smoke
• D. Solid wax (candle body), liquid wax (around the wick) and wax vapour (smoke above the wick) — all three states

Q28. Exercise 10 notes that grains of rice and rice flour take the shape of the container they are placed in. Are they solids or liquids?

• A. Liquids, because they take the shape of the container
• B. Liquids, because they flow easily out of the container
• C. Gases, because they fill the container completely
• D. Solids, because each individual grain has a fixed shape and volume; the container shape is taken by the heap of grains, not by individual grains

Q29. Exercise 6 asks for a diagram of particles as ice melts to water and then turns into vapour. The correct sequence of interparticle spacing across the three diagrams should be

• A. Spacing in ice diagram > spacing in water diagram > spacing in vapour diagram
• B. All three diagrams show exactly the same spacing because the substance is the same
• C. Spacing in water diagram > spacing in vapour diagram > spacing in ice diagram
• D. Spacing in ice diagram < spacing in water diagram < spacing in vapour diagram, with the vapour particles widely separated

Q30. When a metal block at room temperature is heated steadily, at what stage do its constituent particles begin to leave their fixed positions?

• A. When the metal block changes colour to red
• B. Only after the metal block has cooled down again
• C. As soon as heating begins, even at room temperature
• D. When heating raises the particle vibrations to a level vigorous enough to overcome interparticle attractions, i.e., near the melting point