Nature of matter

Iron, copper, and gold are metals and show typical metallic properties such as lustre, conductivity, and malleability. Option D is the closest distractor because silicon, boron, and arsenic are metalloids, not metals. Exam tip: for a group-based question, check the classification of every element in the option.

Oxygen, carbon, and sulfur are all non-metals, so option B is correct. Boron, silicon, and germanium are metalloids, not non-metals. Sodium, iron, copper, aluminium, gold, and silver are metals. Exam tip: elements near the zig-zag boundary between metals and non-metals in the periodic table are generally metalloids.

Boron, silicon, and germanium are metalloids. Metalloids show some properties of both metals and non-metals; for example, silicon is a semiconductor. Sodium, potassium, and calcium are metals, so option B is not a group of metalloids. Exam tip: metalloids are generally found near the zig-zag boundary between metals and non-metals in the periodic table.

Brittleness means that a substance breaks on hammering or applying pressure instead of undergoing significant deformation. Most solid non-metals, such as sulphur, are brittle. Option B describes ductility, while option C describes malleability; these properties are generally associated with metals. Exam tip: remember brittleness for non-metals and ductility/malleability for metals.

Sulfur is a solid non-metal at room temperature and is brittle, meaning that it tends to break or crumble when struck rather than being beaten into sheets. This makes sulfur the correct example, so option A is correct. Copper, gold and aluminium are metals; in general, metals are malleable and ductile, although their exact physical properties vary. Copper and aluminium can be drawn into wires, while gold is especially malleable. The question tests the general classification and physical properties of elements, not whether every metal behaves identically in every situation. Thus the three metallic choices are plausible substances but do not represent a brittle non-metal in this context.

The governing concept is the connection between a material’s physical properties and its practical use. Iron is a hard, strong, and tough metal, so it can withstand hammering and remain firm after being shaped into a nail. Its metallic nature also contributes to strength and durability. Option A is therefore the best answer. A nail is made from a solid material, so option B is impossible. Complete brittleness would cause the material to crack during shaping rather than form a useful nail, making option C unsuitable. Iron is not completely soluble in water, so option D is unrelated. The answer links hardness and metallic strength with the use.

Silver is a metal, and its surface reflects light, giving it a metallic lustre. Oxygen and chlorine are gaseous non-metals, while sulphur is a non-metal and does not generally show metallic lustre. Exam tip: lustre, malleability and electrical conductivity are common properties of metals.

Carbon is a non-metal and occurs as a solid at room temperature. Its common allotropes include graphite and diamond. Bromine is also a non-metal, but it is liquid at room temperature; sodium and mercury are metals. Exam tip: remember the usual states of non-metals—carbon is solid, bromine is liquid, and most other non-metals are gases.

Copper is a metal that conducts electricity very well and is ductile. Its ductility allows it to be drawn into thin wires, so it is widely used for electrical wiring. Chlorine, sulphur, and nitrogen are non-metals and are not suitable for making ordinary electrical wires. Exam tip: for wire-making, remember both conductivity and ductility.

The governing concept is the classification of matter into elements, compounds, and mixtures, with metals and non-metals being types of elements. Oxygen consists only of oxygen atoms and therefore is an element; it is specifically a non-metal. Brass is a homogeneous mixture, or alloy, of mainly copper and zinc. Air is a mixture of gases, principally nitrogen and oxygen, while salt water is a mixture of salt dissolved in water. Thus, option C is the only element. The word “metal” is a distractor because oxygen is not a metal, but the question asks for an element, not necessarily a metal.

Brass is a homogeneous mixture of copper and zinc, so it is an alloy. An alloy is generally a mixture of two or more metals, or of a metal with another element. Pure gold is an element, and oxygen and sulfur are also elements; therefore, they are not alloys. Exam tip: brass, bronze and steel are common examples of alloys.

The direct answer is A: heat conductivity, more precisely thermal conductivity. Cooking utensils must receive heat from a flame or heating surface and transfer it to the food. Metals generally conduct heat well, so heat spreads through a metal pan more effectively than through a poor conductor. Step by step: the flame supplies heat; the metal base absorbs and conducts it; the food receives heat and cooks. Option A is correct. Option B, bitter taste, is not a useful property of utensils and is not a general property of metals. Option C, extreme brittleness, would make a utensil break easily, so it would be undesirable. Option D, gaseous state, is wrong because ordinary cooking utensils need to be solid and retain their shape. Some handles may use poor conductors to reduce heating, but the pan itself is useful because of metal’s thermal conductivity. Remember: pan body conducts heat; handle is often insulating.

Phosphorus is a non-metal. It is placed in Group 15 of the periodic table and generally forms covalent compounds, a characteristic property of non-metals. Metalloids show a mixture of metallic and non-metallic properties, whereas phosphorus is not a metalloid. Exam tip: remember nitrogen and phosphorus in Group 15 as non-metals.

The governing concept is the classification of elements according to their physical and chemical properties. Germanium, symbol Ge, is placed near the metal–non-metal boundary in the periodic table and is classified as a metalloid. Metalloids show a combination of properties: they may have a metallic appearance, yet their electrical conductivity is intermediate and can vary with conditions. Germanium is therefore useful as a semiconductor material. It is not a mixture, because it is a chemical element, and it is not classified simply as a metal or non-metal. Hence option C is correct; the other choices ignore its intermediate character or its elemental identity.

Metals generally conduct electricity while non-metals usually do not. Exam tip: compare using properties.

Metalloids are elements that have properties intermediate between metals and non-metals. For example, silicon has some metallic characteristics but can also behave as a semiconductor, like non-metals in certain respects. Option A is incorrect because metalloids do not show only metallic properties. Exam tip: remember silicon and germanium as common examples of metalloids.

Metal non-metal and metalloid are classes based on chemical nature. Exam tip: always identify the basis of classification.

The direct answer is A: a difference in the physical properties of the components. A mixture contains substances that are together but not chemically joined into one new substance. Their physical properties, such as particle size, boiling point, solubility, density or magnetism, can be used for separation. Step by step: identify a property in which the components differ; choose a method based on that difference; carry out the method; collect the separated components. Option A is correct. Option B is wrong because having the same colour does not help us distinguish or separate components. Option C is wrong because mixture components need not be elements; they may be compounds or elements. Option D is wrong because components do not disappear during ordinary separation; they are recovered in different portions. For example, filtration uses particle-size difference, distillation uses boiling-point difference, and chromatography uses differences in solubility and movement. Remember: separation changes location, not the identity of the components.

The direct answer is B, magnetic separation. A mixture of sand and iron filings contains two solids with different properties. Iron is attracted by a magnet, but ordinary sand is not. Place the mixture on paper and move a magnet, preferably covered with paper or plastic, over it. The iron filings will cling to the magnet and the sand will remain behind; removing the cover releases the iron. Option A, filtration, is used mainly to separate an insoluble solid from a liquid, so it is not the simple choice here. Option B works because it uses iron’s magnetic property. Option C, evaporation, separates a dissolved solid from a solution by removing liquid, which is not this mixture. Option D, condensation, changes vapour into liquid and does not separate these two solid substances. Remember: iron plus a magnet means magnetic separation. This answer and explanation are consistent and factually sound.

In filtration, the mixture is passed through filter paper. An insoluble solid such as sand remains on the paper as residue, while the liquid passes through as filtrate. Distillation is more suitable for separating liquids or obtaining a solvent from a solution. Exam tip: for a sand–water mixture, choose filtration.

The governing concept is separation of a dissolved solid from a solution by using a difference in volatility. In salt water, sodium chloride is dissolved in liquid water, so the salt particles are too small to be retained by ordinary filter paper. On heating or leaving the solution in suitable conditions, water changes into vapour and escapes, whereas salt remains as a solid residue. This process is evaporation, so option A is correct. Magnetic separation requires a magnetic component, hand picking requires visible solid pieces, and filtration is useful for an insoluble solid, not for salt that has already dissolved.

The governing concept is separation based on differences in boiling points and volatility. During distillation, a liquid mixture is heated; the component with the lower boiling point vaporises more readily. The vapour is then cooled in a condenser and collected as liquid, while the less volatile component remains behind or distils later. Therefore option B, distillation, is correct. Filtration separates an insoluble solid from a fluid and cannot normally separate two miscible liquids. Magnetic separation needs magnetic properties, and sorting is a mechanical method for visibly different solid pieces. If the liquids have very close boiling points, fractional distillation is preferred, but the general method asked here is distillation.

In simple distillation water vaporises and then condenses. Exam tip: think of distillation when solvent is required.

The governing concept is sublimation, a change of state in which a suitable solid changes directly into vapour without first becoming a liquid. When a mixture contains one sublimable solid and another non-sublimable solid, gentle heating allows the first substance to vaporise; cooling a suitable surface can deposit it again as a solid, leaving the other component behind. Thus option A is correct. Filtration uses a porous barrier, sedimentation allows heavier particles to settle under gravity, and decantation pours off the clear liquid above a settled solid. Examples of sublimable substances include camphor and ammonium chloride, although the exact conditions depend on the substance.

Ammonium chloride sublimes but sand does not. Exam tip: choose this method when only one component is sublimable.