Question 1
Which metal is commonly used for food packaging because it is cheap and can be made into thin sheets: aluminium, copper, iron, or gold?
Steps only
Aluminium is malleable and can be made into foil.
Answer
(i) Aluminium.
CLASS 7 · SCIENCE · CHAPTER 4
The World of Metals and Non-metals
Simple answers to all 12 end questions, with sample results and explanations for the chapter’s metal and non-metal investigations.
18 worked answersComplete chapter answers
18 worked answers · short steps first, explanations when you need them
Let Us Enhance Our Learning
Textbook pages 37–39
Question 2
Which metal catches fire when it comes in contact with water: copper, aluminium, zinc, or sodium?
Steps only
Sodium reacts very strongly with water and may catch fire.
Answer
(iv) Sodium.
Question 3
State True or False and give a reason: (i) Aluminium and copper are non-metals used for utensils and statues. (ii) Metal oxides in water turn blue litmus red. (iii) Oxygen is a non-metal needed for respiration. (iv) Copper vessels are used for boiling water because copper conducts electricity well.
Steps only
(i) F (ii) F (iii) T (iv) F
Answer
False, False, True, False.
Question 4
Why are only a few metals suitable for making jewellery?
Steps only
Jewellery metals should be shiny, easy to shape, durable, and attractive.
Answer
Gold and silver are lustrous, malleable, ductile, and resist corrosion.
Question 5
Match the uses with the jumbled names: electrical wiring; most malleable and ductile; needed for life; helps plants grow when added through fertilisers; used in water purification. Names: ENXYGO, NECOHIRL, PPEPORC, TENGOINR, OGDL.
Steps only
(i) c, (ii) e, (iii) a, (iv) d, (v) b
Answer
Copper, gold, oxygen, nitrogen, chlorine.
Question 6
What happens when oxygen reacts with magnesium and sulfur? How do the products differ in nature?
Steps only
Magnesium oxide is basic; sulfur dioxide dissolved in water is acidic.
Answer
Metal oxide—basic; non-metal oxide—acidic.
Question 7
Complete the flowchart showing what happens when magnesium burns and the product is tested with litmus.
Steps only
Magnesium + air + heat → magnesium oxide; + water → basic mixture; red litmus turns blue.
Answer
Blue litmus: no change. Red litmus: turns blue.
Question 8
Which listed material would you choose for a pan to boil water: iron, copper, sulfur, coal, plastic, wood, or cardboard? Why?
Steps only
Copper is a strong heat conductor; iron can also be used. The non-metals listed are unsuitable.
Answer
Copper (or iron) is suitable because it conducts heat.
Question 9
Three iron nails are dipped separately in oil, water, and vinegar. Which nail will not rust, and why?
Steps only
Oil-coated nail: oil blocks air and water, which iron needs in order to rust.
Answer
The nail dipped in oil should not rust.
Question 10
How do the properties of metals and non-metals determine their everyday uses?
Steps only
Uses depend on properties: copper wires, aluminium foil, iron tools, oxygen for respiration, chlorine for water treatment.
Answer
A material is useful when its properties fit the task.
Question 11
Zinc protects iron from rust by coating it. Since sulfur does not react with water, can sulfur be used instead? Justify your answer.
Steps only
Sulfur is brittle and would not form a strong, continuous protective layer.
Answer
No. Sulfur is not a durable coating for iron.
Question 12
Why does an ironsmith heat iron before making tools?
Steps only
Hot iron is softer and easier to hammer into shape.
Answer
Heating makes iron easier to shape.
Chapter investigations and learning prompts
Textbook pages 40–54
Question Activities 4.1–4.3
What would you observe when copper, aluminium, iron, coal, sulfur, and wood are inspected, hammered, dropped, or compared for heat conduction?
Steps only
Metals flatten, ring, and conduct heat; coal and sulfur break; wood is a poor heat conductor.
Answer
Copper, aluminium, and iron show common metal properties.
Question Activity 4.4
Which listed materials should make a simple battery-and-lamp tester glow, and what does that show?
Steps only
Metals (aluminium, iron, copper) conduct; the other listed materials are poor conductors.
Answer
A glowing lamp shows that the test material conducts electricity.
Question Activity 4.5
In the three-bottle iron-nail experiment, which conditions are present and where should rust form?
Steps only
Only bottle C has both air and water, so rust forms there.
Answer
Both air and water are needed for iron to rust.
Question Activities 4.6–4.8
What are the observations when magnesium and sulfur burn, and how do their oxides behave in water?
Steps only
Magnesium oxide is basic; sulfur dioxide in water is acidic.
Answer
Metal oxide: basic. Non-metal oxide: acidic.
Question Section 4.5
Give examples of non-metals that are important in everyday life and state their uses.
Steps only
Oxygen—respiration; nitrogen—fertilisers; chlorine—water purification; iodine—antiseptic; carbon—living matter.
Answer
Non-metals also have many important uses.
Question Exploratory Projects
Suggest a way to complete the projects on Indian metal art, metal-producing regions, metals in phones, and responsible metal use.
Steps only
Research each project with reliable sources; explain material uses and include responsible mining and recycling.
Answer
Use evidence and give credit for research and permitted images.