Nature of matter

The governing definition of matter is anything that has mass and occupies space, or volume. Solids, liquids, and gases all satisfy this definition because they consist of particles and have measurable mass and volume. Therefore option A is correct. Producing light is not essential for matter: many material objects are non-luminous, although a luminous object can still be matter. Sound is a form of energy and requires a medium for its transmission; it is not itself the definition of a substance. An idea is abstract and has no physical mass or volume. This definition is the basic starting point for distinguishing material substances from energy, sensations, and concepts.

Air is matter because it has mass and occupies space. For example, air filled in a balloon increases its weight and occupies the balloon’s volume. Sound is a form of energy, and a shadow is produced when light is blocked; therefore, neither is matter. Exam tip: A substance is matter if it has mass and occupies space.

Light is a form of energy and not space-occupying matter. Mass and volume are needed for matter.

Matter is anything that has mass and occupies space; the space occupied is its volume. Therefore, mass and volume are the basic identifying properties of matter. Colour, taste, smell, and shine are not present in every substance. Exam tip: Remember the standard definition: matter has mass and occupies space.

Air is considered matter because it consists of gases such as nitrogen, oxygen, argon, and small amounts of other substances; these particles possess mass and occupy volume. Although air is usually invisible, invisibility does not remove its material nature. Option A is therefore correct. Its effects can be demonstrated by weighing an inflated balloon, observing that air fills a container, or compressing air in a syringe. Air is not merely energy, and it is not sound: sound is a mechanical disturbance travelling through a medium, while air is the material medium that can carry it.

The direct answer is A: solid, liquid and gas are the three common states of matter. Matter is anything that has mass and occupies space. In a solid, particles are closely packed and the substance usually has a fixed shape and volume. In a liquid, particles can move past one another, so the liquid has a fixed volume but takes the shape of its container. In a gas, particles are far apart, so it has neither a fixed shape nor a fixed volume. Option A gives these physical states and is correct. Option B lists forms of energy or physical phenomena, not states of matter. Option C lists properties detected by the senses, not states. Option D classifies elements or substances as metals, non-metals and metalloids; that is a different classification based on chemical properties. A substance can change from one state to another when temperature or pressure changes. Memory cue: solid keeps shape, liquid flows, gas fills space.

In the solid state, particles are closely packed and only vibrate about fixed positions. Therefore, a solid has both a definite shape and a definite volume. A liquid has a definite volume but changes its shape according to its container. Exam tip: definite shape and definite volume together indicate a solid.

A liquid has nearly definite volume but takes the shape of its container. This is a key property of liquids.

A gas has neither a definite shape nor a definite volume because its particles are relatively far apart, move freely, and spread throughout the available container. It therefore takes the container’s shape and expands to occupy its volume, making option D correct. A solid has strong particle attraction and retains both a definite shape and a definite volume. A liquid has a nearly definite volume but flows and takes the shape of its container. A particle is not one of the three classical states of matter; it is a constituent unit that may form matter in any state. Thus only gas satisfies both conditions stated in the question.

Ice is the solid state of water. Its particles remain arranged around relatively fixed positions, so it has a definite shape and definite volume. Liquid water has a definite volume but changes its shape according to the container. Exam tip: water, ice, and water vapour are examples of liquid, solid, and gaseous states respectively.

Steam is water in its gaseous state, so gas is the correct answer. Its particles are relatively far apart, and it can spread to fill the container. Liquid water has a fixed volume, whereas steam does not. Exam tip: The solid, liquid, and gaseous forms of water are ice, water, and steam respectively.

Liquid water is in the liquid state. A liquid has a definite volume but takes the shape of the container in which it is kept. A solid has both definite shape and definite volume, so it is not the correct option. Exam tip: definite volume but no fixed shape identifies a liquid.

Particles of matter are in continuous motion. In solids, they vibrate about fixed positions, whereas in liquids and gases they move more freely. Option A is incorrect because even particles in a solid vibrate. Exam tip: particle motion generally increases when temperature increases.

The particle theory of matter states that particles are not packed into one continuous, gapless substance; there is space between them. The amount of interparticle space varies: it is generally smallest in solids, greater in liquids, and greatest in gases. Therefore, option A is correct. This concept helps explain diffusion, the mixing of particles without continuous stirring, and compression, especially in gases where the gaps can be reduced. Light or sound may travel through a material under suitable conditions, but neither is the universal substance occupying the spaces between all particles.

In the solid state, particles are very close together and vibrate about fixed positions, so the interparticle attraction is generally the greatest. It is weaker in liquids and much weaker in gases and plasma, where particles are far apart. Exam tip: Remember the usual order of attraction: solid > liquid > gas.

In the gaseous state, the force of attraction between particles is very weak, so the particles remain far apart. Therefore, gases occupy a large volume and can be compressed easily. Particles are closest in solids, while their separation in liquids is greater than in solids but less than in gases. Exam tip: Remember the order of interparticle distance—solid < liquid < gas.

In a solid, particles are closely packed with very little empty space between them. On applying pressure, there is almost no space left to bring the particles closer, so solids are difficult to compress. Option A is more characteristic of gases, which have large spaces between their particles. Exam tip: Compressibility depends on interparticle space—the less the space, the lower the compressibility.

Gas particles are far apart, so there is a large amount of empty space between them. When pressure is applied, this empty space is reduced and the particles come closer; the actual size of the particles does not normally decrease. In solids and liquids, particles are much closer together, so they are less compressible than gases. Exam tip: Link the high compressibility of gases with the large intermolecular spaces between their particles.

Odour particles move spontaneously from a region of higher concentration to regions of lower concentration. This process is called diffusion, so diffusion is the correct answer. Sublimation is the direct change of a solid into a gas, whereas here gaseous odour particles are already spreading through the room. Exam tip: Diffusion is fastest in gases because their particles move more freely.

Ink particles spread on their own among water particles. This process is called diffusion and shows that particles of matter are continuously moving and have spaces between them. Option D is incorrect because liquid particles do have some intermolecular space. Exam tip: The spontaneous spreading of colour or smell in a medium is usually an example of diffusion.

When temperature increases, the average kinetic energy of the particles increases, so they generally move faster. Particle motion does not stop on heating; complete cessation is considered only ideally at absolute zero. Exam tip: remember that temperature is related to the average kinetic energy of particles.

In hot water, water and sugar particles have greater kinetic energy, so they move faster and collide more frequently. This helps sugar particles spread through water more quickly, increasing the rate of dissolution. Spaces between particles exist in matter, but they are not the main reason for faster dissolving in hot water. Exam tip: Increasing temperature generally increases particle motion and the rate at which most solids dissolve.

Physical classification groups matter according to its observable physical state, mainly solid, liquid, or gas. Therefore, option B is correct. This grouping is based on properties such as shape, volume, particle spacing, and freedom of particle movement, without requiring a change in chemical composition. A chemical formula identifies composition, atomic number identifies the number of protons in an element, and molecular mass gives a mass value; none of these is the primary basis for the basic physical classification of matter. The word physical is the key clue because the classification uses physical form and behaviour.

The governing concept is that chemical classification depends on the composition and chemical identity of matter, not on its colour, size, or the speed of its particles. Matter is first considered as a pure substance or a mixture. A pure substance has a fixed composition and may be an element or a compound, whereas a mixture contains two or more substances whose proportions may vary. For example, oxygen is an element, water is a compound, and air is a mixture. Therefore, option C is correct. Particle motion and physical appearance can describe matter, but they do not determine its chemical classification.

On the basis of composition matter is divided into pure substance and mixture. This is basic classification.