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

Matter is made up of extremely small particles that cannot be seen with the naked eye. These particles form the basic structure of all substances. Even fine chalk powder or sugar, when ground or dissolved, eventually breaks down into these constituent particles.

Grinding chalk into powder does not create a new substance. It only reduces the size of chalk without altering its chemical composition. It is refers to this as a physical change where the original substance remains the same despite changes in appearance or form.

When sugar dissolves in water, its particles separate and occupy spaces between water molecules. Although the sugar seems to disappear, its taste remains. This supports the idea that matter is composed of tiny, invisible particles that continue to exist in solution.

All matter has particles with some space between them. These spaces allow substances like sugar to dissolve or gases to compress. Interparticle spaces are critical in understanding how matter behaves in different states. 

Solids are formed because their constituent particles are held tightly by strong attractive forces. These interparticle attractions prevent the particles from moving freely and give solids their definite shape and volume, as explained through examples of rock salt and metal.

Acharya Kanad, an ancient Indian philosopher, proposed the idea that all matter is made of indivisible particles called Parmanu. This early atomic theory, recorded in the Vaisheshika Sutras, laid the foundation for understanding the particulate nature of matter.

Solids, particles are closely packed and held by strong forces. This restricts them to only vibrate in place, giving solids a fixed shape and volume. They do not flow like liquids or gases due to this tight arrangement.

At the melting point, particles in a solid vibrate vigorously due to heat. When they gain enough energy, they overcome interparticle forces and begin to move freely, transitioning the substance into the liquid state while maintaining the same composition.

The melting point of ice is 0°C. This is the temperature at which ice melts to form liquid water under normal atmospheric pressure, marking a change in the physical state without altering the chemical composition.

Liquids do not have a fixed shape. They take the shape of their containers because their particles are loosely packed and can move past each other. However, they maintain a fixed volume, as shown through container transfer activities in the chapter.

Gas particles are widely spaced and have negligible interparticle attractions. This allows them to be compressed easily when external pressure is applied, unlike solids or liquids which have limited space between particles.

At its boiling point, water’s particles gain enough energy to overcome attractive forces. This leads to rapid formation of vapour not just at the surface but throughout the liquid. The boiling point is the temperature where this rapid change occurs.

Both solids and liquids have a definite volume. Solids also have a fixed shape, while liquids do not. Gases, however, have neither fixed shape nor fixed volume due to maximum interparticle spacing.

Particles in a gas move rapidly and randomly in all directions.
This property enables them to spread and occupy all available space in a container, unlike solids and liquids which have more restricted particle movement.

The incense stick activity shows how gaseous fragrance particles spread across the room.
It demonstrates diffusion—movement of particles from high to low concentration—which is possible because of the free movement of gas particles in air.

Diffusion, such as the spreading of ink in water or fragrance in air, shows that matter is made up of particles.
These particles move and mix on their own, providing evidence that matter is not continuous but composed of tiny moving entities.

When sugar is dissolved in water, its particles occupy the spaces between water particles.
As proof of interparticle space. Despite adding solid sugar, the water level does not increase much, which supports the presence of tiny spaces between particles in liquids.

All states—solid, liquid and gas—particles exert some attractive force on one another.
These forces are strongest in solids, weaker in liquids and weakest in gases. This attraction keeps matter together and influences its physical state.

Heating provides energy to the particles in a solid, making them vibrate faster. When they gain enough energy to overcome the strong interparticle attraction, the solid melts and changes into a liquid.
This transformation due to heat is a physical change.

Melting point as the temperature at which a solid starts turning into a liquid. It is a fixed temperature for pure substances.
For example, the melting point of ice is 0°C, which is when it begins to convert into liquid water.

Solids have a rigid and definite shape because their particles are tightly packed with very little space between them. The strong interparticle forces and minimal movement make solids firm and less compressible compared to other states.

Gas particles move the fastest because they possess the most kinetic energy. Their rapid, random motion and weak intermolecular forces allow them to spread quickly and fill any container.
This high energy explains diffusion and compressibility in gases.

Gases consist of fast-moving particles that are far apart from each other. Due to weak or negligible attractions, gas particles spread to fill any available space, making gases shapeless and allowing their volume to change easily under pressure.

Solid, liquid and gas as the three common physical states of matter. Flame is not a state of matter; it is a visible effect of a chemical reaction such as combustion. The content focuses only on the three classical states.

Potassium permanganate crystals dissolving in water and spreading throughout as a vivid illustration of particle movement. The slow spreading of color shows that particles of both the crystal and the water are constantly moving and mixing.

In ancient Indian philosophy, “Parmanu” was described as the smallest indivisible part of matter. Acharya Kanad with proposing that everything in the universe is composed of these tiny particles, an early form of the atomic theory still taught today. 

Liquids, particles are not as tightly packed as in solids. This looser arrangement allows them to move past one another, giving liquids the ability to flow and take the shape of their containers while maintaining volume.

Sublimation is a process mentioned in the chapter where certain solids like camphor or iodine convert directly into gas without becoming liquid. This change bypasses the liquid state and illustrates another example of how particle behavior differs between substances.

Particles of matter possess kinetic energy due to internal motion. This internal energy causes them to remain in constant motion, whether vibrating in solids, sliding in liquids or moving freely in gases. The chapter attributes this motion to the energy present within particles.

Gases can be poured and take the shape of a container because their particles move randomly in all directions. This movement enables them to spread and fill spaces, making gases flow in a way similar to liquids.