Nature of matter

The governing concept is the physical state of matter, which describes how particles are arranged and how freely they move under given conditions. In a solid, particles are closely packed and mainly vibrate about fixed positions, so the substance has a definite shape and volume. In a liquid, particles remain close but can flow, giving a definite volume and no fixed shape. In a gas, particles are far apart and move freely, so it has neither a fixed shape nor a fixed volume. Therefore, option A—solid, liquid, and gas—is correct. Metals, non-metals, and metalloids classify elements, while elements, compounds, mixtures and acids, bases, salts are different chemical classifications.

In the solid state, particles are closely packed and the force of attraction between them is strong. Therefore, a solid has both a fixed shape and a fixed volume. A liquid has a fixed volume but no fixed shape because it takes the shape of its container. Exam tip: fixed shape together with fixed volume indicates a solid.

A liquid has fixed volume but changes shape with the container. Exam tip: use water as a common example.

A gas fills the container so it has no fixed shape or volume. Exam tip: remember expansion ability.

Oil is a liquid because it flows and takes the container shape. Exam tip: flow is a key sign of liquids.

The governing concept is the state of matter determined by temperature and pressure. At ordinary room temperature and normal atmospheric pressure, iron exists as a solid. Its particles are held in an ordered arrangement by strong metallic bonding and mainly vibrate around relatively fixed positions. Consequently, iron has a definite shape and definite volume under ordinary conditions. It becomes liquid only after being heated to its melting point, which is far above normal room temperature, and it would require still more extreme conditions to become a gas. Therefore, option A is correct. Liquid, gas, and mist are not the normal state of a pure iron sample kept at ordinary temperature.

At normal temperature and atmospheric pressure, oxygen
(O_2
) is in the gaseous state, so option C is correct. Its boiling point is about
-183^
\circ\mathrm{C}
; therefore, at normal temperature it is not a liquid. Exam tip: compare the given temperature with a substance’s melting point and boiling point to identify its physical state.

The governing concept is change of physical state without change in chemical identity. Ice and liquid water are both H₂O, so their molecules have the same composition and the same chemical identity. The difference is that ice is the solid state, in which molecules occupy a more fixed arrangement, whereas water is the liquid state, in which molecules can move past one another. Heating or cooling can bring about this reversible change of state without changing H₂O into a different substance. Therefore, option B, physical state, is correct. Colour, element, and atomic number do not describe the main difference: water and ice are not different elements, and a change from solid to liquid does not alter atomic numbers.

Steam is the gaseous state of water because, on heating, water molecules gain enough energy to spread out as a gas. Liquid water flows and has a definite volume, whereas steam can fill its container. Exam tip: ice, water and steam represent the solid, liquid and gaseous states respectively.

The arrangement of particles differs in the three common states of matter. In a solid, particles are held very close together by strong forces and occupy fairly fixed positions. They can vibrate, but they do not move freely from place to place. This produces a definite shape and volume. Liquid particles are close but less regularly arranged, while gas particles are far apart and move freely.

Therefore, option C, solid, is correct. The phrase “most ordered and close” points directly to the solid state. A gas has the least orderly arrangement, and smoke is a mixture of particles dispersed in a gas rather than a basic state with the required arrangement. Crystalline solids show particularly regular order, but among the given states, solid is the proper answer.

The governing concept is the particle nature of matter. In a gas, particles are separated by comparatively large empty spaces and move freely in all directions. When pressure is applied, the particles can be pushed closer together, so the volume decreases substantially without changing the particles themselves into another substance. This is why a syringe, balloon, or gas cylinder can contain a gas under compression. Option A is correct because it identifies the large intermolecular spaces. Option B describes neither the normal motion of gas particles nor the reason for compressibility. Colour and heaviness, mentioned in C and D, do not determine whether a gas can be compressed.

The governing concept is the arrangement of particles in different states of matter. In a solid, particles are held closely together by strong attractive forces and occupy nearly fixed positions. Only a very small amount of empty space exists between them, so ordinary pressure cannot reduce the volume appreciably. Therefore, option B is correct: closely packed particles leave little room to move closer. Option A is the opposite of the actual arrangement in a solid and would describe a gas more closely. Option C is false because solids may be hot, cold, or at room temperature. Option D concerns light emission, which has no connection with compressibility. The important link is close packing plus strong attraction.

Particles in a liquid are close together but can slide past one another. Therefore, a liquid can flow and takes the shape of its container. A liquid does not have a fixed shape; that is a property of solids. Exam tip: liquids have a fixed volume but not a fixed shape.

On physical-state basis matter is classified as solid liquid and gas. Exam tip: read the basis carefully.

Candle wax is a solid at normal temperature because it has a definite shape and volume, with its particles held closely together. On heating, wax melts and becomes a liquid; therefore, liquid is not its state at normal temperature. Exam tip: always identify the state of a substance at the temperature specified in the question.

In a solid, particles are closely packed and the force of attraction between them is relatively strong. Therefore, a solid has both a fixed shape and a fixed volume. Filling the entire container is a property of gases, and transparency is not a necessary property of all solids. Exam tip: identify a solid by its fixed shape and fixed volume.

Gas particles have large spaces between them and move freely in all directions. Therefore, a gas expands to occupy the entire volume of its container. A fixed shape is a property of solids; gases can flow, and their particles are not closely packed. Exam tip: a gas has neither a fixed shape nor a fixed volume.

The governing concept is the physical state of a substance at ordinary temperature and pressure. Under normal classroom conditions, water exists as a liquid: it has a definite volume but takes the shape of its container and can flow. Therefore, option C is correct. Helium in a normal environment is a gas, so option A is not suitable. Glass is a solid, even though it can be shaped when heated strongly, and an iron nail is also a solid; these are the substances in options B and D. The word “normal” means that the usual ambient conditions are intended, not extreme pressure or temperature. State is identified here by observable properties such as flow and shape.

In the gaseous state, the force of attraction between particles is very weak and the spaces between them are relatively large. Therefore, gas particles move most freely in all directions. Liquid particles can flow, but their intermolecular attraction is greater than in gases. Exam tip: the usual order of freedom of particle motion is solid < liquid < gas.

The governing concept is the kinetic-particle model of solids. In a solid, particles are held by strong attractive forces in an orderly arrangement. They cannot normally travel freely from one place to another, but they continuously vibrate about their mean or fixed positions because they possess thermal energy. The amplitude of this vibration generally increases when temperature rises, while the solid still retains its overall shape. Thus option A is correct. Option B describes neither normal solid motion nor the effect of confinement. Option C violates conservation of matter, since particles do not simply disappear. Option D is also incorrect because the vibrations occur in different directions, not only upward. Fixed positions do not mean complete absence of motion.

Gases are highly compressible due to large empty spaces. Exam tip: understand gas properties from particle distance.

Wood is a solid because its particles are relatively close together and it has a definite shape and definite volume. Milk is a liquid, whereas steam and carbon dioxide are gases; gases have neither a definite shape nor a definite volume. Exam tip: a substance with definite shape and definite volume is a solid.

The governing concept is the classification of matter by its observable physical state. Milk flows, can be poured, and takes the shape of the vessel containing it; these are characteristic properties of a liquid. Therefore, option B is correct under ordinary conditions. Scientifically, milk is also a colloidal mixture containing water, fat droplets, proteins, sugars, and minerals, but its bulk behaviour is liquid, so it is classified as a liquid in this school-level question. It is not a solid merely because it contains suspended particles. Option C is unsuitable because milk does not fill its container as a gas, and option D requires an ionized, high-energy state not found in ordinary milk. Option A is therefore also incorrect.

Smoke contains tiny particles and gases so it is matter. Exam tip: focus on mass more than visibility.

In solids particles are close so attraction is high. Exam tip: study closeness and attraction together.