Physical Properties of Metals and Non-Metals – Long Answer Questions (CBSE Class 10 Science)

Medium Level (Application & Explanation)

Q1. Compare the hardness of metals and non-metals. Explain with examples how this property affects their uses, and mention key exceptions.

Answer: Most metals are hard, meaning they resist scratching and cutting, so they are suitable for structures and tools. For example, iron (Fe) is hard and used in bridges and buildings, while copper (Cu) is moderately hard and used in wires. However, there are exceptions: sodium (Na) and potassium (K) are so soft they can be cut with a knife, so they are stored carefully and not used for structural work. Most non-metals are soft or brittle, such as sulphur (S) and phosphorus (P), which break or crumble, making them unsuitable for load-bearing. A famous exception is diamond (a form of carbon), the hardest natural substance, used in cutting tools. Thus, hardness helps us select materials: hard metals for strength, soft non-metals for specialized uses, and exceptions must always be remembered.

Q2. What is metallic lustre? Explain why most metals are shiny and give exceptions among non-metals with examples.

Answer: Metallic lustre is the shiny appearance of metals. It occurs because free electrons in metals can absorb and re-emit light, giving a bright, reflective surface. This is why gold (Au) has a yellow shine and is used in jewellery, silver (Ag) has a brilliant white shine and is used in mirrors and ornaments, and aluminium (Al) looks silvery and is used in foil and utensils. Metals are often polished to increase their lustre for decorative or reflective uses. Among non-metals, most are dull, but there are exceptions. Iodine (I₂) is a shiny, crystalline non-metal. Graphite (a form of carbon) looks shiny on smooth surfaces, though it is soft and black. Therefore, while lustre is a typical metallic property, some non-metals can appear shiny, so we must confirm with other properties too.

Q3. Differentiate between malleability and ductility. Explain their importance with suitable examples and a simple activity
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Answer:

Malleability is the ability of a material to be hammered or rolled into thin sheets. Gold and silver are highly malleable, used to make gold leaf and decorative sheets. Aluminium is malleable and used to make kitchen foil.
Ductility is the ability to be drawn into wires. Copper is very ductile, used for electrical wiring, and aluminium is used in power cables.

Importance:

These properties make metals ideal for manufacturing, packaging, wiring, and sheet metal work. Non-metals like sulphur and coal are brittle, so they break when hammered and cannot be made into wires.

Activity link:

In the malleability/ductility test, copper flattens without breaking and stretches into wire, while sulphur/coal crumbles. Hence, metals are malleable and ductile, but most non-metals are not.

Q4. Why are metals good conductors of heat and electricity? Explain with examples and include one non-metal exception.

Answer: Metals have free-moving electrons that carry electric charge and transfer heat efficiently. This is why they are good conductors. Silver (Ag) is the best electrical conductor, though expensive; copper (Cu) is commonly used in household wiring; aluminium (Al) is used in power lines due to its low density and good conductivity. In a simple circuit, a copper wire quickly lights a bulb because it offers a low-resistance path. Most non-metals are poor conductors as they lack free electrons. A key exception is graphite (carbon), which conducts electricity due to delocalized electrons between its layers and is used in electrodes. Therefore, for electrical and thermal applications, metals are preferred, while graphite remains a rare non-metal exception.

Q5. Explain the melting/boiling points and density trends of metals and non-metals. Include important exceptions and uses.

Answer: Most metals have high melting and boiling points due to strong metallic bonds, and they usually have high density because their atoms are closely packed. For example, iron melts around 1538°C, and tungsten has an extremely high melting point (about 3400°C), making it suitable for high-temperature uses. Gold and lead feel heavy due to high density. However, exceptions exist: mercury (Hg) is a liquid at room temperature (melting point about –39°C), and sodium (Na) and potassium (K) have relatively low melting points and are soft. Most non-metals have low melting/boiling points and low density; many like oxygen (O₂) and nitrogen (N₂) are gases at room temperature. An exception is diamond (carbon), with an extremely high melting point and very high hardness. These trends guide material selection for heat, strength, and weight-sensitive uses.

High Complexity (Analytical & Scenario-Based)

Q6. You must choose materials for four tasks: a bridge beam, household wiring, a temple bell, and food packaging foil. Justify each choice using physical properties.

Answer:

Bridge beam: Choose iron/steel because metals are hard, strong, and have high density and high melting points, allowing them to bear heavy loads without deformation. Non-metals like sulphur are brittle and unsuitable.
Household wiring: Choose copper (Cu) due to high electrical conductivity, ductility (can be drawn into thin wires), and adequate strength. Silver is better but costly; aluminium is lighter but less conductive than copper.
Temple bell: Choose bronze (a metal alloy) because metals are sonorous; they produce a clear ringing sound when struck. Non-metals are non-sonorous and brittle.
Food packaging foil: Choose aluminium (Al) for its malleability (thin foil), low density (lightweight), and metallic lustre (reflects heat/light). Thus, each selection matches a key physical property required by the task.

Q7. Design a step-by-step plan to classify unknown samples as metals or non-metals using simple school-lab tests. Explain what observations will confirm your conclusion.

Answer: Plan:

Hammer test (Malleability): Gently hammer small pieces.
- Metals: Flatten into sheets without breaking.
- Non-metals: Crack or powder (brittle).
Wire drawing (Ductility) or bending: Try to stretch or bend a thin strip.
- Metals: Can be drawn/bent without snapping.
- Non-metals: Snap or crumble.
Conductivity test (Circuit with bulb):
- Metals (e.g., Cu, Al): Bulb glows.
- Non-metals (e.g., S, P): No glow; exception: graphite conducts.
Sound test (Sonority): Tap with a metal rod.
- Metals: Ringing sound.
- Non-metals: Dull thud.
Optional: Appearance (Lustre):
- Metals: Shiny, more so when polished.
- Non-metals: Dull; exception: iodine appears shiny.

Conclusion:

If most tests show malleable, ductile, conductive, sonorous, lustrous, classify as metal. If brittle, non-conductive, non-sonorous, classify as non-metal, while noting exceptions like graphite and iodine.

Q8. “All metals are hard and all non-metals are soft.” Analyse this statement using examples, exceptions, and how property knowledge affects real-life choices.

Answer: The statement is incorrect and oversimplified. While many metals are hard (e.g., iron used in structures), some are soft: sodium (Na) and potassium (K) can be cut with a knife. Many non-metals are soft or brittle (e.g., sulphur crumbles), but diamond (carbon) is the hardest natural substance and is used in cutting tools. Property knowledge affects real-life choices: we choose copper for wires due to ductility and conductivity, bronze for bells due to sonority, and aluminium for foil due to malleability and low density. Non-metals like oxygen (O₂) and nitrogen (N₂) are gases, showing that non-metals vary widely. Therefore, always match the required property with the material, and remember key exceptions to avoid wrong selections.

Q9. A city plans new overhead power lines. Should it use copper or aluminium conductors? Evaluate using conductivity, density, ductility, and practical needs.

Answer: Both copper (Cu) and aluminium (Al) are good conductors of electricity, but the choice depends on multiple physical properties. Copper has higher electrical conductivity and is highly ductile, making reliable wires. However, aluminium has lower density (is lighter), which reduces weight and mechanical load on poles and towers over long distances. Aluminium is also sufficiently ductile for cables and is commonly used in transmission lines because it balances good conductivity with low mass, enabling long spans. For short-distance indoor wiring, copper is often preferred due to better conductivity and compact size. Thus, for overhead city transmission, aluminium is generally the practical choice, while copper suits household wiring. The decision aligns with the properties of conductivity, density, and ductility.

Q10. Your school museum arranges elements by color. Explain why color alone cannot classify metals and non-metals. Suggest better tests and justify with examples.

Answer: Color is not a reliable classifier because both metals and non-metals can share s...