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Electric wires are coated with insulating materials such as PVC (polyvinyl chloride) or rubber to prevent electric shock when touched. The coating does not conduct electricity, so it acts as a safety barrier, preventing current from passing through the body. While it may offer some protection against rust (if the metal core is copper, it doesn’t rust easily) and doesn’t primarily prevent heating or melting, its main function is to prevent electric shock.
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Diamond is an unusual material — it is a poor conductor of electricity because it has no free electrons, but it is an excellent conductor of heat due to its strong covalent bonding and high lattice vibrational conductivity (phonon transport). Copper, mercury, and lead are metals, so they conduct both electricity and heat well. This unique property makes diamond valuable in heat sinks for electronics.
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Malleability is the property of a metal that allows it to be hammered or rolled into thin sheets (foils) without breaking. For example, gold and silver are highly malleable. Ductility is the ability to be drawn into wires. Sonority is the property of producing sound when struck. Conductivity is the ability to allow heat or electricity to pass through.
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Non-metals are generally poor conductors of heat and electricity (with the notable exception of graphite, an allotrope of carbon). They lack free electrons (delocalised electrons) that are responsible for conductivity in metals. Non-metals are neither malleable (they are brittle) nor ductile. They are typically insulators or semiconductors.
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The characteristic shiny appearance of a freshly cut or polished metal surface is called metallic lustre. This occurs because metals reflect light efficiently due to the presence of free electrons. Malleability (ability to be hammered into sheets), sonority (ability to produce sound), and ductility (ability to be drawn into wires) are different physical properties, not related to shine.
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Copper is widely used for electrical wiring because it is an excellent conductor of electricity (second only to silver). This allows electric current to flow with minimal resistance and energy loss. Wood is an insulator and does not conduct electricity, so it cannot be used for wiring. While copper has lustre and is heavy, these are not the primary reasons for its use in wiring; conductivity is the key property.
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The simplest and most accessible way to begin classifying substances into metals and non-metals is by observing their physical properties such as appearance (lustre), hardness, conductivity, malleability, and ductility. These properties can be observed without complex laboratory equipment or chemical reactions. Atomic number and molecular mass require advanced knowledge; chemical reactions are more complex and may destroy the sample.
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Hardness is not a constant property across all metals. Different metals have different hardness levels. For example, sodium is soft enough to be cut with a knife, while iron is much harder, and tungsten is extremely hard. Hardness depends on the metal’s atomic structure, bonding, and crystal lattice, not on colour or size alone. Thus, hardness varies from metal to metal.
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Gold is the most ductile metal. One gram of gold can be drawn into a wire nearly 2 km long (about 1.8–2 km) because of its exceptional ductility. While copper and aluminium are also ductile, they cannot be drawn into such a long wire from just one gram. Iron has lower ductility. This property of gold is exploited in gold leaf and fine wire applications.
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Metals are excellent conductors of heat. This property allows cooking vessels to transfer heat quickly and evenly from the stove to the food being cooked. Shine (lustre) and appearance are secondary, and heaviness is not an advantage (it can make handling difficult). The primary functional requirement for cookware is efficient heat conduction, which metals like copper, aluminium, and stainless steel provide.
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Graphite is an allotrope of carbon and a non-metal that is a good conductor of electricity. This is due to the presence of delocalised (free) electrons in its layered hexagonal structure, which can move along the layers. Sulphur, phosphorus, and iodine are poor conductors (insulators). Graphite’s conductivity makes it useful in electrodes, brushes for motors, and as a lubricant.
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Ductility is the property of metals that allows them to be stretched or drawn into thin wires without breaking. This is due to the metallic bonding where layers of atoms can slide past each other. Gold, silver, and copper are highly ductile. Brittleness is the opposite (breaking under tension), hardness relates to resistance to scratching, and lustre relates to shine. Ductility is specifically about wire formation.
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Copper and aluminium are highly ductile metals, so they are commonly available and used in the form of wires for electrical wiring, cables, and other applications. While they can also be found as sheets, rods, or powders, the most common commercial form for these metals (especially copper) is wire. They are solid at room temperature, not liquid or gas.
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Malleability is the property that allows metals to be hammered, pressed, or rolled into thin sheets without cracking or breaking. When a metal is struck with a hammer, its shape changes because the metal atoms can slide past each other due to metallic bonding. This property is distinct from ductility (drawing into wires). Hardness and density do not directly cause shape change under hammering.
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Sonority is the property of metals to produce a ringing sound when struck. This is why metals are used in making bells, gongs, and musical instruments like cymbals. Ductile (can be drawn into wires), malleable (can be hammered into sheets), and lustrous (shiny) are different properties. Sonorous is specifically related to sound production.
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Thermal conductivity is the property that allows heat to pass through a material. Metals have high thermal conductivity because free electrons can transfer kinetic energy rapidly throughout the metal. This property is essential for cooking vessels, as it allows heat from the stove to transfer quickly to the food. Lustre (shine), sonority (sound), and hardness (resistance to scratching) do not contribute to heat transfer.
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The word “sonorous” comes from the Latin word “sonorus” meaning noisy or sounding. In chemistry, it describes the property of metals to produce a deep, ringing sound when struck. This is why metal bells, gongs, and coins produce sound. Sonority has no direct relation to heat, light, or electricity (though some metals also conduct electricity well, that is a separate property).
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Metal surfaces often develop a thin layer of oxide (corrosion) or accumulate dust/grease over time. These layers can act as insulators, preventing proper electrical contact and giving a false negative result in conductivity tests. Sandpaper removes this layer, exposing the fresh metal surface for good electrical contact. While sandpaper also makes the metal shiny, that is a secondary effect, not the primary purpose.
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Malleability is the specific property that enables metals to be hammered or rolled into thin sheets without breaking. Examples include gold leaf (beaten into extremely thin sheets) and aluminium foil. Conductivity is for heat/electricity, sonority is for sound, and ductility is for drawing into wires. The key phrase “beaten into thin sheets” directly defines malleability.
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School bells are made of metals (typically brass, bronze, or steel) because metals produce a loud, clear, ringing sound when struck – a property called sonority. This sound carries well and is pleasing. Non-metals, if struck, would produce a dull thud or break (being brittle). Metals are not necessarily light (bells are heavy), not soft (they are hard), and not brittle (they are tough).
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The ability to shape metals into various forms comes from two related properties: malleability (hammering into sheets) and ductility (stretching into wires). These properties arise from metallic bonding, which allows layers of atoms to slide past each other without breaking. Hardness, density, colour, shine, melting point, and mass do not directly confer the ability to change shape; they may even hinder it.
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Gold and silver are the most malleable metals. One gram of gold can be hammered into a sheet of about 1 square metre (gold leaf). Silver is also extremely malleable. Copper and aluminium are malleable but less so than gold and silver. Iron and zinc are moderately malleable. Mercury is liquid at room temperature (not malleable). Malleability decreases roughly with increasing hardness.
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Non-metals generally lack free electrons, which are responsible for efficient heat transfer in metals. Therefore, most non-metals are poor conductors of heat (they are thermal insulators). Examples include wood, plastic, sulphur, and phosphorus. (Graphite is an exception, being a good conductor, but it is not typical of non-metals overall.) Non-metals are also not malleable or ductile; they are brittle.
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Oxygen (O₂), carbon (C in graphite/diamond forms), and sulphur (S) are all non-metals. Option A contains iron, copper, aluminium (all metals). Option C contains sodium, potassium, calcium (all metals, specifically alkali and alkaline earth metals). Option D contains zinc, lead, tin (all metals). Therefore, only option B consists entirely of non-metals.
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Non-metals generally do not have a shiny, reflective surface; they appear dull (except iodine which has some lustre and graphite which may appear shiny). Softness (many non-metals are soft, e.g., sulphur), brittleness (non-metals are generally brittle), and hardness (some non-metals like diamond are very hard) can be shown by non-metals. However, metallic lustre is a characteristic property of metals, not non-metals.
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Most non-metals exist either as solids (e.g., carbon, sulphur, phosphorus, iodine) or gases (e.g., oxygen, nitrogen, hydrogen, chlorine, fluorine) at room temperature. Only one non-metal, bromine, is a liquid at room temperature. Therefore, “solid or gaseous forms” correctly describes the majority. Plasma form is not found under normal conditions; “solid only” excludes gases; “liquid only” is incorrect.
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PVC (polyvinyl chloride) is a plastic that is an electrical insulator (poor conductor of electricity). Coating electric wires with PVC prevents current from leaking out and protects people from electric shock. If PVC were a conductor, the coating would be useless. It is not a semiconductor (like silicon) and not a metal. The insulating property is essential for safety.
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The property of producing sound when struck is called sonority. Metals are sonorous due to their crystal lattice structure, which vibrates when struck, producing a ringing tone. Shiny (lustre) relates to light reflection, heaviness (density) does not cause sound, and hardness (resistance to scratching) is not directly responsible for sound production. Sonority is the correct technical term.
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Pure metals in their freshly cut, polished, or cleaned state have a characteristic shiny or lustrous surface. This is due to the presence of free electrons that reflect light efficiently. However, many metals tarnish over time when exposed to air (e.g., iron rusts, silver blackens, copper turns green), but the pure metal itself is shiny. The question specifies “pure state,” so shining surface is correct.
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Oxygen is essential for respiration in most living organisms. It is a non-metal and a poor conductor of electricity (it is an insulator in its gaseous form). Chlorine is toxic and not used for respiration, hydrogen is flammable and not breathable, and nitrogen is inert and does not support respiration (though it is a major component of air). Oxygen fits both criteria.
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Silver has the highest thermal conductivity of all metals, followed closely by copper. Both are excellent heat conductors. While iron, aluminium, mercury, lead, and zinc conduct heat well compared to non-metals, they are not the best. Silver and copper are the top two. This is why copper is used in cookware bottoms and heat exchangers, and silver is used in high-end thermal applications.
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In NCERT Class 8 Science (Chapter 4: Materials: Metals and Non-Metals), a common activity involves hammering a metal piece (e.g., iron nail or aluminium foil) to see if it can be flattened into a sheet without breaking. This tests malleability. Ductility is tested by trying to draw a wire, conductivity by a bulb circuit, and sonority by striking the metal. Hammering specifically tests malleability.
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The primary reason iron, copper, and other metals are used for cooking utensils is their high thermal conductivity, which allows heat to transfer quickly and evenly from the stove to the food. Shine (lustre) is aesthetic, heaviness is not an advantage, and while some metals are relatively cheap (iron), copper is more expensive; cost is not the main reason. Heat conduction is functional.
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PVC (polyvinyl chloride) is a plastic that is an excellent electrical insulator. It is widely used as a coating (insulation) for copper and aluminium electrical wires to prevent short circuits and electric shocks. Metal would conduct electricity (unsafe), glass is too brittle and heavy, wood is not flexible enough. PVC is flexible, durable, and safe, making it the standard choice.
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Metals are generally good conductors of electricity because they contain a sea of delocalised (free) electrons that can move easily when an electric field is applied. Silver is the best conductor, followed by copper, gold, and aluminium. This property makes metals essential for electrical wiring, circuits, and components. They are not poor conductors, non-conductors, or insulators (the opposite is true for non-metals).
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In a simple circuit with a battery, wires, and a bulb, inserting a metal sample completes the circuit if the metal conducts electricity. If the bulb glows, it indicates that electric current is flowing through the metal sample, meaning the metal is a conductor. The glow does not indicate magnetism (magnetic metals like iron would show a different test), lustre (shine), or malleability (hammering test).
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Metals are typically lustrous (shiny) when freshly cut or polished. This metallic lustre is due to the presence of free electrons that reflect light. Only one metal (mercury) is liquid at room temperature; all others are solids. Non-metals are usually dull. Metals are not brittle (they are malleable and ductile); they are the opposite of brittle. Lustre is a defining characteristic of metals.
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Metals are good conductors of both heat (thermal conductivity) and electricity (electrical conductivity) due to the presence of mobile, delocalised electrons that can transfer kinetic energy (heat) and charge (electricity). While some metals are magnetic (iron, cobalt, nickel), not all are; and while metals are sonorous (conduct sound well), that is not the primary classification. The dual conductivity of heat and electricity is a fundamental metallic property.
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Sodium metal is highly reactive with moisture (including sweat on skin) and air. It reacts vigorously to form sodium hydroxide (caustic) and hydrogen gas, which can ignite or cause burns. Sodium should never be touched with bare hands. It is typically handled with forceps or tongs, often under kerosene oil. Paper or cloth would not provide adequate protection and could catch fire.
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Bromine (Br₂) is the only non-metal that is liquid at room temperature (melting point –7.2 °C, boiling point 58.8 °C). Iodine is a solid (sublimes), carbon is solid (graphite/diamond), and sulphur is solid. Mercury is a liquid metal, but the question asks for a non-metal. Bromine is a reddish-brown, volatile liquid and is hazardous. This is a commonly tested fact in NCERT science.
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Sodium is an extremely reactive metal. It reacts vigorously with oxygen (forming sodium oxide) and water vapour in air (forming sodium hydroxide and hydrogen gas, which can ignite). To prevent this reaction, sodium is stored completely submerged in kerosene oil (or mineral oil), which acts as a barrier against air and moisture. Softness, low melting point, and ductility are not reasons for storage under oil.
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Most metals are malleable (can be hammered into sheets). This is a characteristic property. Non-metals are brittle. Metals are good (not poor) conductors of heat. Metals have a shiny (not dull) appearance when fresh. Therefore, “high malleability” is correct. Malleability, along with ductility, lustre, and conductivity, are hallmark properties of metals.
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In NCERT Class 8 Science, Chapter 4 (Materials: Metals and Non-Metals), Activity 7.7 (or similar numbering depending on edition) typically involves comparing the properties of metals and non-metals through experiments such as testing conductivity, hammering, and appearance. The chapter’s theme is classification of elements into metals and non-metals based on their physical and chemical properties, not alloys, plastics, or states of matter.
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In a simple circuit with a bulb, if the bulb does not glow when a material is placed in the circuit, it means the material does not allow electric current to pass through it. Such materials are non-conductors or insulators. Most non-metals (except graphite) are insulators. Therefore, the material is likely a non-metal or an insulator. Metals and conductive alloys would make the bulb glow.
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Oxygen is a non-metal (it is a gas at room temperature, poor conductor, not malleable, etc.). Aluminium, copper, and zinc are all metals. This is a straightforward classification question testing the ability to distinguish metals from non-metals. Oxygen is essential for respiration and combustion but is chemically a non-metal.
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Most non-metals are poor conductors of heat and electricity (they are insulators). Graphite is an exception, but it is not “most non-metals.” Dullness (lack of lustre), brittleness (break when hammered), and softness (many non-metals are soft) are common properties of non-metals. However, some non-metals like diamond are very hard. Conductivity is the property most non-metals do NOT show.
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Sodium metal is often stored under kerosene oil. When needed, it is taken out and the excess oil must be removed. Sodium is dried by pressing it gently between folds of filter paper. Filter paper is absorbent and does not react with sodium (unlike cotton cloth or newspaper, which contain moisture and could react). The filter paper absorbs the kerosene without causing a reaction. This is a standard laboratory practice.
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Most metals have high melting points (e.g., iron 1538°C, copper 1085°C, tungsten 3422°C), though some like gallium (30°C) and mercury (–39°C) are exceptions. Most non-metals have low melting points (e.g., oxygen –218°C, nitrogen –210°C, sulphur 115°C), though carbon (diamond sublimes >3500°C) is an exception. The general trend is correctly stated in option C. The other options are false due to exceptions.
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Gold is the most ductile metal. One gram of gold can be drawn into a wire nearly 2 kilometres long (or even longer under ideal conditions). This extreme ductility, along with its malleability, makes gold unique. Silver and copper are also highly ductile, but gold surpasses them. Aluminium is ductile but less so. The NCERT textbook specifically mentions gold as the most ductile metal.Close