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Q1. The coating on electric wires prevents:
Electric wires are coated with insulating materials like PVC or rubber to prevent electric shock when touched. The coating stops the electric current from passing through our body. It does not prevent heating (the wire still heats up), melting (the coating may melt at high temperatures but that’s not its purpose), or rusting (the metal core may rust, but the coating is mainly for insulation). So electric shock is correct.
Q2. Which of the following is a poor conductor of electricity but a good conductor of heat?
Diamond is a non-metal allotrope of carbon. It is a very poor conductor of electricity because it has no free electrons to carry charge. However, it is an excellent conductor of heat — it is even better than many metals. Copper and lead are good conductors of both heat and electricity. Mercury is a metal and a conductor. So diamond is correct.
Q3. Which property allows a metal to be hammered into thin foil without breaking?
Malleability is the property of metals that allows them to be beaten into thin sheets (foils) without breaking. Gold and silver are highly malleable. Ductility is the ability to be drawn into wires. Sonority is the ability to produce sound. Conductivity is the ability to conduct heat or electricity. So malleability is correct.
Q4. Non-metals are generally:
Non-metals are generally poor conductors of heat and electricity because they do not have free electrons to carry charge or heat. Most non-metals are insulators. Graphite is an exception (it conducts electricity). Non-metals are not malleable (they are brittle) and not ductile. So poor conductors is correct.
Q5. The shining surface of metals is called:
The shining appearance of a freshly cut metal surface is called metallic lustre. This property is characteristic of metals. Malleability is the ability to be hammered into sheets. Sonority is the ability to produce sound. Ductility is the ability to be drawn into wires. So metallic lustre is correct.
Q6. Why is copper preferred over wood for making electrical wiring?
Copper is a metal that is an excellent conductor of electricity. This is why it is preferred for making electrical wiring. Wood is an insulator (does not conduct electricity), so it cannot be used for wiring. Copper is not cheaper than wood (wood is cheaper), lustre is not the reason, and being heavier is not an advantage. So copper is a good conductor of electricity is correct.
Q7. The easiest way to start grouping substances is by comparing their:
The simplest way to begin grouping substances is by comparing their physical properties — such as appearance, hardness, lustre, conductivity, etc. These are easily observable without chemical testing. Atomic number and molecular mass require advanced measurements. Chemical reactions require testing. So physical properties is correct.
Q8. The hardness of metals:
Hardness is not the same for all metals — it varies significantly. For example, sodium is soft enough to be cut with a knife, while iron is much harder, and tungsten is extremely hard. Hardness does not depend on colour or size alone. So varies from metal to metal is correct.
Q9. A wire of about 2 km can be drawn from:
Gold is the most ductile metal. One gram of gold can be drawn into a wire that is about 2 km long (some sources say up to 2 km). This is because gold has excellent ductility — it can be stretched into very thin wires without breaking. Iron, copper, and aluminium are also ductile but not as much as gold. So one gram of gold is correct.
Q10. Cooking vessels are usually made of metals because they:
Cooking vessels are made of metals because metals are good conductors of heat (thermal conductivity). This allows heat to spread quickly and evenly through the vessel for cooking. Shiny appearance and attractiveness are secondary reasons. Being heavy is not an advantage. So conduct heat well is correct.
Q11. Which of the following non-metals is a good conductor of electricity?
Graphite is a non-metal allotrope of carbon that is a good conductor of electricity. This is because graphite has free (delocalised) electrons between its layers that can carry electric current. Sulphur, phosphorus, and iodine are poor conductors (insulators). So graphite is correct.
Q12. Metals can be drawn into thin wires due to:
Ductility is the property that allows metals to be drawn into thin wires (like copper wire, gold wire, etc.). Brittleness is the opposite (breaking easily). Hardness is resistance to scratching. Lustre is shine. So ductility is correct.
Q13. Metals like copper and aluminium are available in the form of:
Copper and aluminium are commonly available in the form of wires because they are highly ductile and good conductors of electricity. They are used for electrical wiring. They are not typically available as powders, liquids, or gases (though aluminium powder exists, wires are the most common form for these metals). So wires is correct.
Q14. The shape of metals changes when hammered due to:
Malleability is the property that allows metals to be hammered or beaten into thin sheets without breaking. When a metal is hammered, its shape changes because of its malleability. Ductility is for drawing into wires. Hardness and density are not the reasons. So malleability is correct.
Q15. Metals that produce sound on striking are called:
Sonority is the property of metals that makes them produce a ringing sound when struck. This is why metals are used for making bells, gongs, and school bells. Ductile is for wires, malleable for sheets, lustrous for shine. So sonorous is correct.
Q16. Which property helps metals conduct heat in cooking vessels?
Thermal conductivity is the property that allows metals to conduct heat. This is what makes metals suitable for cooking vessels — heat passes quickly through the metal. Lustre is shine, sonority is sound, hardness is resistance to scratching. So thermal conductivity is correct.
Q17. The term sonorous is related to:
The term sonorous refers to the property of producing sound. Metals are sonorous — they produce a ringing sound when struck. The word comes from “sonus” meaning sound. It is not related to heat, light, or electricity. So sound is correct.
Q18. Before testing electrical conductivity, why are metal samples cleaned with sandpaper?
Metals often have a layer of corrosion (oxide layer) or dust on their surface that can interfere with electrical conductivity testing. Sandpaper is used to clean the surface to ensure good contact with the circuit. Making them shiny is a side effect, not the main reason. Increasing weight or making them soft is not done by sandpaper. So to remove the layer of corrosion or dust is correct.
Q19. Which property allows metals to be beaten into thin sheets?
Malleability is the property that allows metals to be beaten into thin sheets (like aluminium foil, gold leaf). Conductivity is for heat/electricity, sonority is for sound, ductility is for wires. So malleability is correct.
Q20. School bells are made of metals because metals are:
School bells are made of metals because metals are sonorous — they produce a clear, loud, ringing sound when struck. Metals like brass and bronze are commonly used for bells. They are not light (they are heavy), not soft, and not brittle. So sonorous is correct.
Q21. Metals can be given different shapes because of their:
Metals can be shaped into different forms because of two properties: malleability (beaten into sheets) and ductility (drawn into wires). Together, these allow metals to be given various shapes. Hardness and density do not allow shaping. Colour and shine are not shaping properties. Melting point relates to melting, not shaping. So malleability and ductility is correct.
Q22. The most malleable metals are:
Gold and silver are the most malleable metals. Gold can be beaten into extremely thin sheets (gold leaf) without breaking. Silver is also highly malleable. Copper and aluminium are malleable but less so. Iron and zinc are also malleable but less than gold/silver. Mercury is liquid, not malleable. So gold and silver is correct.
Q23. Non-metals are generally:
Non-metals are generally poor conductors of heat (and electricity) because they lack free electrons. They are not malleable (they are brittle) and not ductile. Good conductors is the opposite of what non-metals are. So poor conductors of heat is correct.
Q24. Which set contains only non-metals?
Oxygen, carbon, and sulphur are all non-metals. Iron, copper, aluminium (A) are metals. Sodium, potassium, calcium (C) are metals. Zinc, lead, tin (D) are metals. So the set containing only non-metals is oxygen, carbon, sulphur.
Q25. Non-metals generally do not show:
Non-metals do not have metallic lustre — they are generally dull in appearance (except iodine which has some lustre, but it’s not metallic). Many non-metals are soft (sulphur), brittle (phosphorus), and some are hard (diamond). But metallic lustre is a property of metals, not non-metals. So metallic lustre is correct.
Q26. Most non-metals are found in:
Most non-metals are found either as solids (carbon, sulphur, phosphorus) or gases (oxygen, nitrogen, chlorine). Only one non-metal (bromine) is liquid at room temperature. So solid or gaseous forms is correct.
Q27. Electric wires are coated with PVC because PVC is a:
PVC (Polyvinyl chloride) is a plastic that is an insulator — it does not conduct electricity. It is used to coat electric wires to prevent electric shock and short circuits. It is not a semiconductor (like silicon), not a conductor (like copper), and not a metal. So insulator is correct.
Q28. Metals usually produce sound because they are:
Metals produce a ringing sound when struck because they are sonorous. This is the property of sonority. Shiny refers to lustre, heavy refers to density, hard refers to hardness. So sonorous is correct.
Q29. Metals in their pure state generally have a:
Metals in their pure state have a shiny or shining surface, called metallic lustre. This is because their atoms reflect light well. Some metals may appear coloured (gold, copper), but the general characteristic is shining. They do not have a dull or rough surface in pure form (dullness comes from oxidation). So shining surface is correct.
Q30. Which non-metal is essential for respiration and is a poor conductor of electricity?
Oxygen is a non-metal that is essential for respiration in living organisms. It is also a poor conductor of electricity (as a gas). Chlorine is toxic and not used in respiration. Hydrogen is not used in respiration (it is a fuel). Nitrogen is present in air but not used in respiration (it’s inert). So oxygen is correct.
Q31. The best conductors of heat are:
Silver and copper are the best conductors of heat among metals. Silver has the highest thermal conductivity, followed by copper. Iron and aluminium are good but not the best. Mercury and lead are poor conductors compared to silver and copper. So silver and copper is correct.
Q32. In a typical NCERT activity, which property is tested by hammering a metal piece?
Hammering a metal piece tests its malleability — whether it can be beaten into thin sheets without breaking. Ductility is tested by drawing into wires. Conductivity is tested using a circuit with a bulb. Sonority is tested by striking. So malleability is correct.
Q33. Metals like iron and copper are used for utensils mainly because they:
Iron and copper are used for cooking utensils because they are good conductors of heat — they allow heat to distribute evenly for cooking. Shiny appearance is secondary. Being heavy is not an advantage. While iron is cheap, copper is expensive, so “cheap” is not the main reason for both. So conduct heat is correct.
Q34. Which material is used to coat electric wires?
Electric wires are coated with PVC (Polyvinyl chloride) or rubber — both are insulators. This prevents electric shock. Glass and wood are insulators but are not used for coating wires (they are not flexible). Metal would conduct electricity and cause short circuits. So PVC is correct.
Q35. Metals generally are:
Metals are generally good conductors of electricity because they have free electrons (delocalised electrons) that can move easily through the metal and carry electric current. Non-metals are poor conductors. So good conductors of electricity is correct.
Q36. What does a glowing bulb in a simple electric circuit with a metal sample indicate?
In a simple electric circuit, if the bulb glows when the metal sample is placed between the terminals, it indicates that the metal is a conductor of electricity. The current flows through the metal to complete the circuit. Magnetism, lustre, and malleability are not tested by this setup. So the metal conducts electricity is correct.
Q37. Metals are usually:
Metals are usually lustrous (shiny) in their pure form. They are not gaseous (except mercury, which is liquid, but most are solid), not dull (they become dull due to corrosion but are shiny in pure state), and not brittle (they are malleable and ductile). So lustrous is correct.
Q38. Metals are good conductors of:
Metals are good conductors of both heat and electricity due to the presence of free electrons. They conduct light only if polished (reflection), but that’s not called conductivity. Magnetism is a separate property (only some metals are magnetic). Sound is not conducted — metals are sonorous (produce sound). So heat and electricity is correct.
Q39. Sodium metal should always be handled with:
Sodium metal is highly reactive and can burn the skin on contact (it reacts with moisture to form sodium hydroxide, which is caustic). It should always be handled with tongs (metal forceps) for safety. Bare hands, paper, or cloth are not safe because sodium can react with moisture. So tongs is correct.
Q40. The only non-metal that exists in liquid state is:
Bromine is the only non-metal that exists as a liquid at room temperature. It is a reddish-brown liquid with a pungent smell. Iodine is a solid (sublimes to gas), carbon is solid, sulphur is solid. So bromine is correct.
Q41. Why is sodium metal stored under kerosene oil?
Sodium metal is stored under kerosene oil because it reacts very vigorously with air (oxygen) and moisture (water vapour) in the atmosphere. This reaction is highly exothermic and can even catch fire. Kerosene prevents contact with air and moisture. Softness and low melting point are not reasons for storage. Ductility is not relevant. So it reacts vigorously with air and moisture is correct.
Q42. Which of the following is a characteristic property of most metals?
Most metals are highly malleable — they can be hammered into thin sheets. Brittleness, poor heat conduction, and dull appearance are properties of non-metals, not metals. Metals are generally not brittle, are good conductors, and are lustrous (shiny). So high malleability is correct.
Q43. Activity 7.7 compares:
Activity 7.7 in the NCERT textbook is designed to compare the properties of metals and non-metals. It tests properties like lustre, hardness, malleability, ductility, conductivity, and sonority. So metals and non-metals is correct.
Q44. In an electrical conductivity test, if the bulb does not glow, the material is likely a:
In the electrical conductivity test, if the bulb does not glow, it means the material does not conduct electricity. This indicates the material is a non-metal or an insulator (like sulphur, plastic, wood). Conductors (metals) would make the bulb glow. So non-metal or insulator is correct.
Q45. Which of the following is a non-metal?
Oxygen is a non-metal. Aluminium, copper, and zinc are all metals. Oxygen is a gas at room temperature, does not have metallic properties, and is a poor conductor. So oxygen is correct.
Q46. Which property is NOT shown by most non-metals?
Most non-metals are not good conductors of heat and electricity (except graphite for electricity and diamond for heat). They show dullness, brittleness, and softness (some are hard like diamond, but most are soft). So conductivity is NOT shown by most non-metals.
Q47. Sodium metal is dried by pressing it between:
Sodium metal is dried by pressing it between sheets of filter paper. This absorbs the kerosene oil (in which it is stored) and any moisture. Newspaper, tissue paper, or cotton cloth are not used because they may leave fibres or react. So filter paper is correct.
Q48. Which statement is true about the melting points of metals and non-metals?
Most metals have high melting points (e.g., iron, copper, tungsten) because of strong metallic bonds. Most non-metals have low melting points (e.g., sulphur, phosphorus) because of weak van der Waals forces. Exceptions exist (mercury is liquid, diamond has high melting point), but the general trend is that metals have higher melting points than non-metals. So most metals have high melting points, while most non-metals have low melting points is correct.
Q49. The most ductile metal is:
Gold is the most ductile metal. One gram of gold can be drawn into a wire about 2 km long. Silver and copper are also highly ductile but not as much as gold. Aluminium is ductile but less than gold. So gold is correct.