Nature of matter

In a physical property identity of substance does not change. Color density melting point are examples.

A chemical property describes a substance’s ability to undergo a chemical change and form a new substance. For example, rusting of iron and burning of wood are related to chemical properties. Colour, mass, and volume are physical properties because observing or measuring them does not form a new substance. Exam tip: If a new substance is produced, think of a chemical change or chemical property.

A physical property can be observed or measured without changing a substance into a new substance. It describes features such as mass, colour, volume, melting point, boiling point, or density. Density tells us how much mass is present in a given volume, so measuring it does not alter the substance’s chemical identity.

Therefore, density is the correct choice, option C. Flammability and reactivity describe how a substance undergoes chemical change, while rusting is itself a chemical change that forms a new substance. Since density can be measured while the composition remains unchanged, it is a physical property.

Flammability shows tendency to burn and new substances form. Therefore it is a chemical property.

The governing concept is the distinction between physical and chemical properties. A physical property can be observed or measured without changing the substance’s chemical identity or composition. Color can be observed directly, and observing it does not produce a new substance or require a chemical reaction. Therefore option A is correct. A chemical property describes how a substance reacts, such as flammability or reaction with an acid. Nuclear properties concern changes or characteristics of the atomic nucleus, not ordinary visible color. Color is also not restricted to living systems, so it is not merely a biological property. A substance may show a color change during a reaction, but color itself remains a physical property.

A chemical property describes the ability of a substance to take part in a chemical reaction and form one or more new substances. Rusting is not merely a change in appearance. Iron reacts with oxygen and moisture and produces iron oxide, commonly called rust. The original iron is therefore chemically changed.

The correct choice is option B, chemical property. A physical property can be measured without changing composition, but the tendency of iron to rust tells us how it reacts with its surroundings. The options about shape and mass do not describe this reaction. Thus, the tendency to rust is correctly classified as a chemical property.

The governing concept is the difference between physical and chemical properties. A physical property can be observed or measured without changing the chemical identity of a substance. Melting point is the temperature at which a solid changes into a liquid at a specified pressure. During this change, the particles gain energy and their arrangement and movement change, but the molecules remain chemically the same. For example, ice and liquid water are both H₂O, so melting does not produce a new substance. Therefore, option C, physical property, is correct. A chemical property describes the ability to undergo a reaction and form new substances, such as iron reacting with oxygen. “Invisible property” is not a scientific category, and melting point is not restricted to gases.

Boiling point is a physical property related to state change. It can help in substance identification.

Combustion involves chemical reaction and forms new substances. Therefore combustibility is a chemical property.

Mass measures the amount of matter present in an object. Measuring it does not change the chemical identity or composition of the substance, so it is a physical property. A chemical property describes a substance’s ability to undergo a reaction and form new substances. Exam tip: A property observed or measured without chemical change is a physical property.

Volume is the measure of the space occupied by a substance. It can be measured without changing the chemical composition of the substance, so it is a physical property. Volume also depends on the amount of substance and is therefore an extensive property, but among the given options, physical property is the correct classification. Exam tip: A property that can be observed or measured without changing a substance’s identity is generally a physical property.

The governing concept is the dependence of a property on the amount of matter. An intensive property has the same value for a given substance whether the sample is small or large, provided conditions such as temperature and pressure are the same. Density, temperature, pressure, and melting point are common examples. If a sample is divided, these values do not become half. Therefore option D is correct. An extensive property, such as mass, volume, or total energy, does depend on the amount of substance. The other options incorrectly restrict intensive properties to mixtures or gases.

The value of an extensive property changes when the amount of substance changes. For example, the mass and volume of a sample increase when more of the substance is taken. In contrast, intensive properties such as temperature and density do not depend on the amount. Exam tip: Remember mass and volume as standard examples of extensive properties.

Density does not depend on the amount or size of a sample; small and large samples of the same substance have the same density. Hence, density is an intensive property. Mass and volume increase when the amount of matter increases, so they are extensive properties. Exam tip: a property that remains unchanged when the amount of substance changes is intensive.

Mass depends on the amount of matter in a sample. If the amount of a sample is doubled, its mass also doubles; therefore, mass is an extensive property. Density, melting point, and boiling point generally do not change with the amount of substance, so they are intensive properties. Exam tip: A property that changes with the size or amount of the sample is extensive.

Volume is an extensive property because it changes with the amount of substance in a sample. For example, if the amount of the same liquid is doubled, its volume is approximately doubled. In contrast, an intensive property such as temperature does not depend on the amount of substance. Exam tip: A property that changes with sample size or amount is an extensive property.

Density can be a characteristic property of a substance. For the same substance density generally does not change with quantity.

Chemical property tells reaction behavior of a substance. Examples are reaction with acids or burning.

The governing concept is whether a change alters chemical identity. When the shape of an object is changed by cutting, bending, stretching, or moulding, the material remains the same substance and no new chemical composition is produced. This makes the change physical, so option D is correct. A chemical change would create one or more new substances with different compositions, as in burning or rusting. A nuclear change affects atomic nuclei and is unrelated to ordinary shaping. Calling the event “no change” is also incorrect because measurable physical features, especially shape, have changed even though chemical identity has not.

When glass breaks, only its shape and size change; its chemical composition remains the same and no new substance is formed. Therefore, it is a physical change. In a chemical change, a new substance is produced, as in rusting of iron. Exam tip: A change involving only state, shape, or form without formation of a new substance is generally a physical change.

Chemical changes occur when milk turns sour and new substances form. Therefore it is a chemical change.

The governing concept is the formation of new substances during a chemical change. As a fruit ripens, enzymes drive reactions that alter pigments, starches, sugars, acids, aromas, and texture. The resulting changes in colour, taste, smell, and composition are not simply reversed to restore the original unripe fruit. Therefore option C, chemical change, is correct. Ripening may include physical changes in softness, but the chemical reactions are the decisive reason for its classification. It is not merely a change of state, and “no change” is clearly inconsistent with the observable and compositional transformations.

The direct answer is D: dissolving sugar in water and recovering it by evaporation shows a physical change and separation. Sugar dissolves by becoming distributed among water particles, but it does not normally become a new substance. When water evaporates, the sugar remains and can be collected again. The original sugar can therefore be recovered, showing reversibility and physical separation. Option D is correct. A is wrong because dissolving sugar does not always produce a chemical change; ordinary dissolution is treated as physical here. B is wrong because no new substance is required for the process. C is wrong because nuclear change involves atomic nuclei and is unrelated to dissolving or evaporation. The water changes from liquid to vapour, while sugar remains behind. Option D also correctly includes both the nature of the change and the method used to recover the component. Memory cue: recoverable original substance usually indicates a physical change.

When paper burns, new substances such as ash, carbon dioxide and water vapour are formed. Therefore, it is a chemical change. Melting of ice is only a change of state; the substance remains water. Exam tip: If new substances are formed, the change is generally chemical.

Air contains nitrogen, oxygen, argon and carbon dioxide, among other gases. Its composition can vary, so it is a homogeneous mixture, not a compound. Exam tip: classify matter by composition, not by colour.