Material Around Us – Case-based Questions with Answers

CBSE Class 6 Science - Chapter 6: Material Around Us | 20 Case-Based Q&A

CBSE Board Examinations — Systematic Order

Real-life scenarios to test understanding
Application of properties and classification
Practical tests, separation methods and safety
Environmental impact and material selection

Tip: Each case includes a short question and a model answer. Use these for classroom discussions, worksheets or quick revision.

20 Case-Based Questions — Chapter 6

Case 1 — A student drops a glass tumbler and it breaks. She wonders why glass was not used for a child's toy instead.

Question: Explain using the properties of materials why glass is not ideal for toys for young children.

Answer: Glass is transparent and hard but brittle; it can shatter into sharp pieces on impact, posing a safety hazard. For children's toys, materials that are durable, non-toxic, and impact-resistant (like certain plastics or rubber) are preferred to reduce risk of injury.

Case 2 — A kitchen pan made of aluminium heats up quickly and cooks food evenly.

Question: Which property of aluminium explains this, and why is it suitable for pans?

Answer: Aluminium is a good conductor of heat, which allows quick and even heat distribution across the pan. Its light weight and corrosion resistance also make it suitable for cookware.

Case 3 — A teacher pours sugar into warm water and it dissolves quickly, but the same amount added to cold water dissolves slowly.

Question: Use the concept of solubility to explain this observation.

Answer: Solubility of many solids in liquids increases with temperature because higher temperature increases particle motion, allowing more solute particles to interact with the solvent. Therefore, sugar dissolves faster in warm water than in cold water.

Case 4 — A bike tyre becomes harder to pump on a cold morning and feels softer on a hot day.

Question: Explain the reason using particle behaviour in gases.

Answer: On heating, gas particles move faster and exert higher pressure, making the tyre feel firmer; on cooling, particle motion slows and pressure decreases, causing the tyre to feel softer. Temperature affects gas pressure inside the tyre.

Case 5 — A stray iron gate left unpainted begins showing reddish-brown patches over time.

Question: Identify the process and suggest two prevention methods.

Answer: The process is rusting (oxidation) of iron due to exposure to moisture and air. Prevention methods include painting/coating the iron to block moisture and air, and applying oil or using galvanisation (zinc coating).

Case 6 — A student notices that when she places a coin on a soft bar of wax and heats it, the coin sinks slightly but the wax returns to shape when cooled.

Question: Explain what this shows about the properties of wax.

Answer: Wax softens on heating (becomes less rigid) due to increased particle motion, allowing the coin to sink. On cooling, wax hardens and regains shape, demonstrating a reversible physical change (melting and solidifying).

Case 7 — A clear plastic bottle and a glass bottle are used for storing juice. Children prefer the plastic bottle for picnics.

Question: Discuss two reasons, based on material properties, why plastic might be preferred outdoors.

Answer: Plastic is lightweight and less likely to break on impact (flexible or tough depending on the type), making it safer and more convenient for outdoor use. It is also cheaper and shatter-resistant compared to glass.

Case 8 — During a science demo, a teacher pours water containing sand through filter paper and collects clear water below.

Question: Name the separation technique and explain why it works for this mixture.

Answer: The technique is filtration. It works because sand particles are undissolved solids that are larger than the pores of the filter paper and thus are trapped, while water passes through, separating the solid from the liquid.

Case 9 — A wooden chair in a house near the sea starts to warp and shows signs of wear faster than similar chairs inland.

Question: Explain the environmental reason for this and suggest a protective measure.

Answer: Coastal environments have higher moisture and salt in the air, which can cause wood to absorb moisture, swell, and warp, and encourage biological decay. Protective measures include sealing the wood with varnish or paint and using treated or water-resistant wood varieties.

Case 10 — A teacher demonstrates putting a strip of metal and a strip of plastic in a circuit; the bulb lights with metal but not with plastic.

Question: What property causes this difference and how does it inform material choice for electrical wires?

Answer: Metal conducts electricity because it has free electrons that allow current flow; plastic is an insulator and prevents current flow. Therefore, metals (e.g., copper) are used as conducting cores in wires, while plastic is used as an insulating cover for safety.

Case 11 — A student finds that spilling oil on a paper surface forms a translucent patch that does not dry like water.

Question: Explain these observations using solubility and transparency concepts.

Answer: Oil is immiscible with water and does not dissolve in paper; it spreads and makes the paper translucent because oil fills spaces between fibres changing how light passes through. Oil does not evaporate quickly like water, so the patch remains oily and translucent.

Case 12 — Two identical-looking bottles contain different liquids—one floats a small cork, the other does not.

Question: What property explains this and how would you test it?

Answer: Density explains the difference: the liquid in which the cork floats has a higher tendency to support the cork (lower density of cork than the liquid). To test, place the same cork in both liquids and observe floating; measure relative masses for same volume samples to compare densities if equipment is available.

Case 13 — A child tears a sheet of paper easily but a thin metal foil does not tear though both are thin.

Question: Explain why paper tears easily while metal foil resists tearing.

Answer: Tearing depends on tensile strength and structure. Paper fibres are held together but have weak bonds that split under stress, while metal foil has a continuous metallic structure with higher tensile strength and ductility that allows it to deform without tearing easily.

Case 14 — During a picnic, children use paper plates and plastic plates. The paper gets soggy with soup but plastic plate holds it.

Question: Which property accounts for this and how can paper plates be improved for liquids?

Answer: Paper is absorbent because its fibres allow water to soak in, making it soggy. Plastic is waterproof and repels liquids. To improve paper plates, a thin waterproof coating can be applied or waxed paper can be used to resist liquids.

Case 15 — A student observes that a piece of rubber band stretches and returns but a plastic ruler, when bent, snaps.

Question: Contrast elasticity and brittleness using these examples.

Answer: The rubber band shows elasticity — it can be stretched and return to its original shape. The plastic ruler is brittle under bending stress and breaks instead of deforming, showing low flexibility. Materials with high elasticity absorb stress and return to shape, whereas brittle materials fracture.

Case 16 — A chemistry set shows that chalk dissolves slowly in acid but not in water.

Question: Explain this observation and give a classroom-safe demonstration idea.

Answer: Chalk (calcium carbonate) reacts chemically with acids producing soluble salts and carbon dioxide, so it dissolves in acid but not in neutral water. A safe demonstration: place small chalk pieces in vinegar (acid) and observe fizzing and gradual disappearance, illustrating chemical reaction rather than simple solubility.

Case 17 — A bottle left in the sun becomes warm but a metal spoon left next to it feels hotter faster.

Question: Explain this using heat conduction and specific heat capacity concepts in simple terms.

Answer: Metals conduct heat better than many plastics; they gain and transfer heat quickly, so the spoon feels hotter faster. Also, materials have different specific heat capacities — the amount of heat needed to raise temperature; substances with low specific heat (like metal) warm up quickly, while those with higher specific heat warm more slowly.

Case 18 — A paper kite flies high while a small stone cannot, even when thrown with the same effort.

Question: Which material properties explain why the kite flies and the stone does not?

Answer: The kite is lightweight with large surface area relative to mass, allowing air to exert lift; its materials are low density and flexible. The stone is dense and heavy with little surface area for lift, so gravity dominates and it falls. Density and shape influence whether an object can be supported by air.

Case 19 — Students are asked to design a simple bowl that will keep food warm longer. They consider using metal, plastic, or insulated materials.

Question: Which material would be best and why? Suggest a practical design.

Answer: An insulated container (e.g., with a vacuum or foam insulating layer) keeps food warm longer by reducing heat loss. Metal alone conducts heat away, while plastic insulates better but still loses heat. A practical design uses a metal inner for durability and even heating with a surrounding insulating layer (plastic or foam) to reduce heat transfer to the outside.

Case 20 — A student notices that dissolved sugar in tea cannot be separated by filtration but sand can.

Question: Explain why filtration works for sand but not for sugar solution and name a method to recover sugar.

Answer: Sand consists of undissolved solid particles that are larger than filter pores, so filtration traps them. Sugar dissolves to form a true solution where sugar molecules are dispersed at molecular level and pass through filters. To recover sugar, evaporate the water from the solution to crystallise the sugar.

Material Around Us – Case-based Questions with Answers

20 Case-Based Questions — Chapter 6

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