NCERT Solutions for Class 7 Science Chapter 4 the World of Metals and Non Metals (PDF) – 2027

Sudarshan uncle makes items of daily use and farming tools out of iron.

They are made of iron. Wood is used to make the handles wherever needed, and coal is burnt in the furnace to heat the iron.

Sudarshan uncle answers: “I am beating it to shape it into an axe.” Red-hot iron is soft, so each blow of the hammer spreads it into the new shape.

Yes — most metals can be beaten flat. This is exactly the question Activity 4.1 goes on to test.

Copper, aluminium and the iron nail are lustrous and hard; coal, sulfur and wood are non-lustrous and softer.

Prediction: the shiny, hard ones will spread out; the dull ones will shatter. That is exactly what happens.

The lustrous and hard objects are the piece of copper, the piece of aluminium and the iron nail.

No. “Hard and solid” is the general rule for metals, not a law without exceptions.

• Sodium and potassium are metals, yet they are so soft that they can be cut with a knife, like a piece of cheese.
• Mercury is a metal that is a liquid at room temperature — you have seen it in the thermometers of the chapter ‘Temperature and its Measurement’ of Grade 6 Curiosity.

The piece of copper, the iron nail and the piece of aluminium became flat on beating.

• Silver vark on barfi and other sweets — silver beaten until it is thinner than paper.
• Aluminium foil for wrapping rotis and packing food.
• Copper and brass sheets beaten into vessels such as lotas and handis.
• Galvanised iron sheets used for roofs, buckets and trunks.
• Gold leaf used on idols and in traditional decoration.

Because copper is far easier to find and to work than iron. Three reasons together explain it.

1. Copper is found almost pure in nature, and its reddish shine is easy to notice; iron is hidden inside dull, stone-like ore.
2. Copper is easier to extract — it needs a lower temperature; iron needs a much hotter furnace, which took a long time to develop.
3. Copper is softer and can be shaped even when cold; iron must first be made red hot.

The property that makes all this possible is ductility — the property of materials by which they can be drawn into wires.

Obviously not. No one has ever seen a wire of coal or of sulfur, and no one ever will.

The difference is easy to hear.

This property of metals that enables them to produce a ringing sound is called sonority, and metals are said to be sonorous in nature.

Yes, a clear difference. Drop each object from the same small height on to the same hard floor, and listen carefully.

Conclusion: metals are sonorous; coal and wood are not.

Yes — and one thing stands out: the part that sits on the fire is always metal, while the part your hand holds is usually not metal.

• The tawa, kadhai, pressure cooker and patila are made of aluminium, steel, iron or copper.
• Their handles are wood, bakelite or plastic, or the metal handle is wrapped in cloth.

Metals used for cooking vessels: aluminium, iron, copper and steel (a mixture of iron and carbon).

Because metals are good conductors of heat.

The metal spoon gets hotter. Touch the upper end of each spoon after a few minutes and the difference is unmistakable.

It tells us that heat travels easily along the metal spoon and very poorly along the wooden spoon, even though both were dipped in water of the same temperature for the same time.

Yes. The metal rod of the screwdriver is steel, but the handle is made of plastic (or a hard rubber-like material).

Rubber is a poor conductor of electricity, so gloves and shoes of rubber keep the electrician out of the electric circuit.

• Gloves stop electricity from entering through the hands.
• Shoes stop it from leaving through the feet into the ground.

Build the tester first, then use it to test each object.

1. Join a cell, a bulb in a holder and connecting wires so that the circuit has a gap with two free ends.
2. Touch the two free ends together once — the bulb must glow. That check tells you the tester itself is working.
3. Now hold the object to be tested across the gap, so that it completes the circuit.
4. If the bulb glows, electricity has passed through the object.

Write the prediction first, then test. A completed Table 4.2 looks like this.

Yes — a very clear pattern. Every material that made the bulb glow is a metal.

Materials that allow electricity to flow through them easily are called good conductors of electricity. Materials that prevent the bulb from glowing by not allowing electricity to pass through them are called poor conductors of electricity.

The correct condition is the third one — when it comes into contact with both air and water.

Each bottle is designed to allow only one condition. Fill Table 4.3 like this.

Conclusion: both water and air are needed for brown deposits to develop on iron. The nails in bottles A (dry air only) and B (water only) stayed free of deposits, which shows that air alone or water alone cannot cause them. Only the nail in bottle C (air and water) developed brown deposits. So moist air is responsible.

This brown deposit is called rust, and the process of its formation on objects made of iron is called rusting.

Yes — an old copper lota left unused grows a dull green layer, and silver jewellery or a silver spoon slowly turns black.

Gradual deterioration of metal surfaces caused by air, water or other substances is known as corrosion.

The magnesium ribbon burns with a dazzling white flame and changes into a white powder. Collect the powder on a watch glass.

Add a few drops of warm water to the white powder, stir it well and test the solution. It is basic.

Generally, oxides of metals are basic in nature.

Dip both papers, not just one. A substance is proved basic only when the red one turns blue and the blue one is unchanged.

Sodium oxide will be basic in nature, because sodium is a metal and metal oxides are basic.

The solution is acidic — it turns blue litmus paper red, while red litmus paper stays red.

You observe that the solution is acidic in nature — it turns blue litmus red.

No. Iron sitting in water with air around it slowly turns to rust; sulfur left in water does nothing at all.

Generally, non-metals do not react with water.

There is no reaction. The pale yellow sulfur powder simply sits in the water — it does not dissolve, no gas bubbles out, there is no colour change, and the tumbler does not become warm.

• Hospitals — oxygen cylinders help patients who cannot breathe properly on their own.
• Mountaineers and divers carry oxygen cylinders where air is thin or absent.
• Burning — fuels such as coal, wood and cooking gas burn only when oxygen is present.
• Cutting and welding metals with a very hot oxygen flame.
• Aquatic animals such as fish use the oxygen dissolved in water.

(i) Aluminium

(iv) Sodium

Only a few metals, such as gold, silver and platinum, have all the properties jewellery needs:

• Lustre — they have an attractive shine.
• Little or no corrosion — gold and platinum do not corrode; silver tarnishes only slowly and can be polished. Iron would rust and copper would turn green.
• High malleability and ductility — they can be beaten and drawn into fine designs and wires.
• Rare and precious, and safe to wear on the skin.

First unjumble Column II, then match.

Both burn in oxygen and both form an oxide — but one oxide is basic and the other is acidic.

Work backwards from the one box that is filled in. The red litmus turns blue, so the solution is basic, so the ash must be a metal oxide, so the burnt substance must be a metal. The metal of this chapter that burns in air to a white ash is magnesium.

Copper is the best choice, with iron a close and cheaper second. Everything else in the list is unusable.

The nail dipped in oil will not rust.

A material is chosen for a job because of the property the job demands. Change the property and the use changes with it.

No, sulfur cannot be used. Not reacting with water is not enough to make a protective coating.

• Sulfur is a brittle non-metal — not malleable or ductile — so it cannot be spread into a thin, firm layer that sticks to iron. Such a layer would crack and flake off, and moist air would reach the iron.
• Sulfur burns, giving harmful sulfur dioxide gas.

Zinc is a metal that forms a firm, lasting coat on iron, so zinc is used instead.

Because hot iron is far more malleable than cold iron. Heating turns a stubborn block into something that will take a shape under the hammer.

Collage: collect pictures of each style, paste them in four panels on a chart paper, and label each with the style, its state and the metal used.

Use an outline political map of India and one colour or symbol per metal.

Sample answer (closing statement): “Metal in a railway line, a bridge or a hospital serves everyone, but metal used only to show wealth wastes limited ores and harms forests and rivers. So we should reduce luxury use, protect essential use and recycle metals such as iron and aluminium.”