CBSE Class 8 Science Chapter 07 Particulate Nature Of Matter MCQs Set 03

Answer: (B) All matter consists of extremely small, discrete units called constituent particles

Explanation:
Activity 7.1 shows that no matter how finely chalk is ground, each tiny speck remains chalk—the substance does not change into anything else. This repeatedly demonstrates that matter is composed of many extremely small basic units (constituent particles) that retain the original substance's properties even at the smallest observable scale.

Answer: (B) Strong interparticle forces keep particles tightly packed with minimal movement, resulting in a solid; weaker forces allow greater movement and liquid or gaseous states

Explanation:
The chapter explains that interparticle attractions determine the physical state through force strength: solids have very strong attractions holding particles in fixed positions; liquids have slightly weaker attractions allowing some particle movement; gases have negligible attractions permitting free movement. This directly explains why heating (which increases particle energy) can overcome these forces and cause state changes.

Answer: (B) Solid particles are held in fixed positions by strong interparticle attractions and cannot move past each other

Explanation:
The chapter states that in solids, strong interparticle forces hold particles in fixed positions, preventing them from moving freely. When force is applied, particles can only vibrate slightly about their fixed positions but cannot relocate or rearrange permanently, which is why solids maintain their shape and structural integrity.

Answer: (B) Particles gain enough thermal energy to overcome interparticle attractions, enabling them to move away from fixed positions while remaining close together

Explanation:
The chapter describes melting as the point where thermal energy becomes sufficient to weaken interparticle attractions so particles can leave their fixed positions and move more freely, though still within a limited space. This increased mobility and slightly increased interparticle distance distinguish the liquid state from the solid state.

Answer: (C) No fixed shape but fixed volume

Explanation:
The water changes shape to match each container (no fixed shape) but the 200 mL measurement remains constant across all three transfers (fixed volume). This distinguishes liquids from solids (which have both fixed shape and volume) and from gases (which have neither fixed shape nor volume).

Answer: (B) Gas particles have negligible interparticle attractions, allowing them to move freely in all directions and spread throughout available space

Explanation:
The unrestricted spreading of smoke demonstrates that gas particles experience negligible attractive forces between them. With such weak or absent attractions, particles can move freely and independently in all directions, expanding to fill whatever space is available—the defining behaviour of gases.

Answer: (B) Gas particles have a large amount of space between them in their natural state, and this space can be reduced by external pressure but will expand again when pressure is removed

Explanation:
The significant volume decrease shows that substantial empty space exists between gas particles. Upon release of pressure, particles spread apart again because they naturally move to fill available space. This behaviour—compressibility followed by re-expansion—is characteristic of gases having large interparticle distances and weak attractions between particles.

Answer: (B) Parmanu is identical to the concept of constituent particles discussed in the chapter—both describe tiny, fundamental, indivisible units that compose all matter

Explanation:
Both the ancient Parmanu concept and the modern constituent particles represent the same fundamental idea: matter is composed of tiny, indivisible basic units. The chapter's discussion of how chalk, sugar, and other substances are made up of increasingly small particles that cannot be further broken down aligns directly with Kanad's philosophical concept developed centuries earlier.

Answer: (B) Particle movement increases with temperature; heat provides energy that causes particles to move faster and spread dissolved substances more rapidly

Explanation:
The chapter explains that water particles move faster when provided with heat energy. Faster-moving water particles can more quickly pull permanganate particles from the grain and distribute them throughout the liquid. In cold water, particle movement is slower, so the spreading happens gradually. This demonstrates the direct relationship between temperature, particle kinetic energy, and the rate of particle motion.

Answer: (B) Solid, then Liquid, then Gas

Explanation:
In solids, particles are tightly packed with minimum interparticle spacing. Liquids have slightly more spacing because particles can move within a limited area. Gases have maximum spacing with particles spread far apart and moving freely. This ordering directly correlates with the strength of interparticle attractions: strongest in solids, weaker in liquids, negligible in gases.

Answer: (B) Gas particles move constantly in all directions and spread throughout available space, distributing fragrance molecules to all corners of the room

Explanation:
The chapter explains that air particles are constantly moving and colliding with fragrance particles, helping them spread throughout the room. This observable phenomenon of fragrance reaching distant locations demonstrates that gas particles are in continuous random motion and possess the ability to distribute themselves throughout any available space—a key characteristic of gases.

Answer: (C) Ice particles are farther apart, resulting in lower density than water and weaker interparticle attractions than would be expected in a typical solid

Explanation:
Unlike most solids where particles are tightly packed, ice's particles are unusually farther apart because water's particular structure creates a larger interparticle spacing in solid form than in liquid form. This greater spacing corresponds to slightly weaker interparticle attractions and explains why ice is less dense than liquid water and floats—a unique behaviour among solids.

Answer: (C) In the gaseous state, where thermal energy is high enough to overcome interparticle attractions, allowing particles to move freely and independently in all directions

Explanation:
The chapter concludes that in the gaseous state, particles possess enough thermal energy to completely overcome the forces of attraction between them, enabling unrestricted movement in all available space. This free movement in all directions distinguishes gases from solids (vibration only) and liquids (limited movement within restricted space), and represents the highest thermal energy state.

Answer: (C) Sugar dissolves by fitting into interparticle spaces, leaving total volume nearly unchanged; sand does not dissolve and occupies bulk space, increasing total volume significantly. This reveals differences in particle interaction based on substance properties.

Explanation:
• Sugar particles separate and fit into spaces between water particles, so total volume changes minimally
• Sand particles cannot dissolve and instead occupy bulk container space
• Sand's larger final volume indicates the particles remain separated and do not intermix at the molecular level
• This demonstrates that solubility depends on how particles of different substances interact and whether they can occupy interparticle spaces.

Answer: (B) Boiling occurs only at one specific temperature while evaporation occurs at all temperatures and is initially slower and confined to the surface

Explanation:
Evaporation occurs slowly at all temperatures and only at the liquid surface, as individual particles escape. Boiling occurs at a specific temperature (boiling point) where particles throughout the liquid gain enough energy to escape simultaneously, creating visible bubbles throughout the liquid. This fundamental difference in location and rate of vapour formation distinguishes these two phase-change processes.

Answer: (C) Nothing—the chair's identity and physical properties depend entirely on the constituent particles that compose it

Explanation:
The chapter establishes that matter is fundamentally composed of constituent particles held together by interparticle forces. A chair's shape, size, colour, weight, and all other properties arise from the arrangement and properties of these particles. Removing all particles eliminates the substance itself—nothing of the chair would remain, since the chair is entirely defined by the particles that constitute it.

Answer: (B) Water particles are separated by some distance from each other; dissolved sugar particles fit into the spaces between water particles, resulting in a total volume that is less than the sum of the individual volumes of water and sugar before mixing

Explanation:
The chapter explains that the volume of solution (C) is less than the sum of water's initial volume plus sugar's volume (B), which proves interparticle spaces exist in liquid water. Sugar's constituent particles occupy these existing spaces without significantly increasing the overall volume. This is direct evidence that liquid particles maintain distance between them rather than being in absolute contact.

Answer: (B) Strong interparticle attractions and fixed particle positions that prevent particles from moving past each other

Explanation:
Strong interparticle forces hold particles firmly in place, and the fixed positions prevent particles from rearranging or moving past one another. When force is applied, particles can only vibrate slightly about their fixed locations—they cannot relocate. This combination of strong attractions and fixed positioning directly explains why solids resist deformation and maintain shape.

Answer: (C) Gas particles are in constant motion, move freely in all directions, and possess negligible interparticle attractions, allowing them to spread and fill all available space

Explanation:
The spontaneous and complete spread of smoke throughout the available space demonstrates that gas particles move independently without being held together by appreciable forces. Their continuous motion in random directions drives them to explore and eventually fill every region of the container space, illustrating the defining characteristics of the gaseous state.

Answer: (B) Particles gain sufficient thermal energy to break free from fixed positions and move within a limited space while remaining relatively close together due to still-significant interparticle attractions

Explanation:
At the melting point, heat energy enables particles to overcome much of the interparticle attraction, allowing them to leave their fixed positions and move more freely. However, attractions remain strong enough to keep particles relatively close and confined to a limited space (characteristic of liquids) rather than free expansion. This intermediate state of particle freedom distinguishes liquids from both solids and gases.

Answer: (B) The empty spaces between constituent particles of one substance that can be occupied by particles of another substance when dissolved

Explanation:
Interparticle spaces are the gaps between particles of a substance. Despite particles being tightly packed in solids or moderately packed in liquids, some space remains. When sugar dissolves, its constituent particles fit into and occupy the interparticle spaces between water molecules. This concept explains how one substance can dissolve into another without necessarily causing a large increase in total volume.

Answer: (B) Particles gain energy to vibrate in fixed positions (solid), then overcome attractions to move in limited space (liquid), then overcome all attractions to move freely in all directions (gas)

Explanation:
The chapter's concluding explanation establishes a clear progression: in solids, low thermal energy restricts movement to small vibrations; as heat is added, particles gain energy to overcome attractions and move within limited space (liquid); with further heating, particles gain enough energy to overcome attractions completely and move freely (gas). This progression directly links thermal energy to observable changes in particle behaviour and macroscopic state properties.

Answer: (C) No matter how finely a substance is divided physically, the constituent particles retain the properties of the original substance, demonstrating that matter possesses a particulate structure composed of identical or similar units

Explanation:
The chapter emphasizes that grinding chalk is a physical change where only the size reduces, not the substance itself. This repeated observation across activities shows that matter maintains its fundamental identity through any physical subdivision. Each chalk particle remains chalk because all pieces contain the same constituent particles arranged in the same way, just in smaller configurations. This supports the particulate model of matter.

Answer: (B) Liquid water particles are already closely packed with minimal interparticle spaces, so compression cannot reduce volume significantly; gases have large interparticle spaces that can be compressed, but liquids cannot

Explanation:
The chapter notes that water is 'practically incompressible' because liquid particles are already relatively close together with very little space between them. Compression force cannot push particles closer when minimal space exists. In contrast, gases have substantial interparticle spacing that can be reduced by applied pressure. This difference in compressibility reveals the difference in interparticle spacing between liquids and gases.

Answer: (C) Liquid particles can move and rearrange, but only within a limited space defined by the liquid's container, neither fixed in position like solids nor free to move in all directions like gases

Explanation:
The chapter explains that liquid particles are free to move relative to each other and can rearrange their positions, allowing the liquid to flow and take the shape of its container. However, they remain confined to a specific volume and do not escape into available space like gas particles do. This intermediate degree of freedom—neither fixed (solid) nor completely unconfined (gas)—is what characterizes the liquid state and explains liquids' properties of definite volume but no fixed shape.