NCERT Solutions Class 7 Science Chapter 4 the World of Metals and Non Metals

F R E E S T U D Y M AT E R I A L F O R E V E R Y S T U D E N T

CLASS 7 · SCIENCE

NCERT Solutions

Chapter 4: The World of Metals
and Non-metals

NCERT Textbook — Curiosity

BOOK PAGES SECTIONS QUESTIONS MEDIUM

41 – 56 20 54 English

Solutions, notes, sample papers & more at 46 pages

Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

CLASS 7 · SCIENCE · CURIOSITY

NCERT Solutions — Chapter 4: The World of Metals and
Non-metals
Complete NCERT Solutions for Class 7 Science Chapter 4 The World of Metals and Non-metals from the
NCERT textbook Curiosity. Every question of the chapter is answered — the ironsmith conversation on pages
41 and 42, all eight Activities 4.1 to 4.8, the Holistic Lens question on iron and Indian civilisation, every in-
text question from pages 43 to 54, the twelve questions of Let Us Enhance Our Learning and the four
Exploratory Projects — with the observation, the reason behind it, filled-in Tables 4.1, 4.2 and 4.3, and the
completed flow chart of Question 7.

TEXTBOOK BOOK PAGES

Curiosity (Class 7) 41 – 56

SECTIONS QUESTIONS

20 54

MEDIUM

English

In-text Questions — Pages 41 & 42
Yashwant and Anandi visit the ironsmith

IN-TEXT

Q1 Yashwant: Which items do you generally make?

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

KIND OF ITEM EXAMPLES HE NAMES

Household items of daily use Flat pans (tawas), buckets (baltis), tongs (chimtas)

Farming tools Spades (phawras), axes (kulhadis), trowels (khurpis), rakes (jelees)

Why it happens: all of these need to be strong and to hold an edge or a shape. Iron is
hard and tough, so a khurpi can cut into soil day after day without bending out of
shape, and a tawa can be heated on the fire again and again without cracking.

Page 1 of 46

Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

Q2 Anandi: What materials are they made of?

Three materials are used in the ironsmith's workshop, each for a different reason.

Iron — the metal from which the item itself is made. It is hard, strong and can be beaten into
shape.
Wood — used to prepare the handles wherever required, because wood is a poor conductor
of heat and does not burn the hand.
Coal — burnt in the furnace to heat the iron until it is red hot and soft enough to be
hammered.

Did you know? Coal is a non-metal (mostly carbon). So even a workshop that is all
about a metal cannot run without a non-metal.

Q3 Anandi is amazed and asks, “Why are you beating it?”

Sudarshan uncle answers: “I am beating it to shape it into an axe.”
He first heats the iron block in the coal furnace until it becomes red hot. Hot iron is much softer
than cold iron, so each blow of the hammer spreads and bends the metal a little instead of
merely bouncing off it. Blow after blow, the shapeless block becomes the flat, wedge-shaped
blade of a kulhadi.

Why it happens: iron is malleable — it can be beaten into a new shape without
breaking. Heating makes it far more malleable. A piece of coal treated the same way
would simply shatter.

Q4 Anandi: Wow, a piece of iron can be beaten into a flat shape! Can we do this with
other metals as well?

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

Page 2 of 46

Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

Copper, aluminium, iron → flatten on hammering → malleable

Coal, sulfur → break into pieces → brittle

Wood → neither flattens nor breaks → neither malleable nor brittle
Gold and silver are the most malleable metals of all.

Check it yourself: look at the silver vark on a barfi. That sheet is a metal beaten so
thin that it tears at a touch — proof of how far a metal will spread under a hammer.

Activity 4.1: Let us explore — Page 42

Page 3 of 46

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Class 7 Science Chapter 4 The World of Metals and Non-metals
g l AglaSem · NCERT Solutions

Section 4.1.1 Malleability
co m
em.
m as
ACTIVITY

.co a g l
a s em the chapter ‘Materials Around Us’ in the Grade 6 Science textbook Curiosity and
gl
Recall
a
Q1
observe the appearances of the above items. Are they lustrous? Also, note whether the
hard or soft and record your observations in Table 4.1.

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m . ag
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S.NO. ag APPEARANCE
OBJECT/MATERIAL HARD/SOFT EFFECT OF
(LUSTROUS/NON- HAMMERING
LUSTROUS)
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(FLATTENS/BREAK

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3. Iron nail

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4. Piece of coal
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Block of wood
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6.

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Table 4.1: Appearance, hardness, and effect of hammering on different objects or materials
(blank, as printed on page 43).

se m
com g l a
m . a
ase
agl

Look at each item in good light before you touch the hammer. Try to scratch it with your nail,
then with an iron nail, to judge hard or soft.

co m
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m a s e
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a g l Page 4 of 46

Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

S.NO. OBJECT/MATERIAL APPEARANCE (LUSTROUS/NON- HARD/SOFT
LUSTROUS)

1. Piece of copper Lustrous (reddish-brown shine) Hard

2. Piece of aluminium Lustrous (silvery shine) Hard

3. Iron nail Lustrous (greyish shine) Hard

4. Piece of coal Non-lustrous (dull black) Soft, crumbly

5. Lump of sulfur (pea- Non-lustrous (dull yellow) Soft
sized)

6. Block of wood Non-lustrous Softer than the
metals

Tip: an old copper or aluminium piece may look dull because of a coating formed in
air. Rub it once with sandpaper and the true metallic lustre appears — judge the
fresh surface, not the old one.

Page 5 of 46

Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

Q2 Now, place each of these items one by one on any hard surface and beat them with a
hammer (Fig. 4.2). What do you think will happen? Do the objects become slightly flatte
or do they break into pieces? Record your observations in Table 4.1.

Fig. 4.2, page 42 — beating an iron nail with a hammer (redrawn sketch).

S.NO. OBJECT/MATERIAL APPEARANCE HARD/SOFT EFFECT OF
(LUSTROUS/NON- HAMMERING
LUSTROUS) (FLATTENS/BREAK
INTO PIECES)

1. Piece of copper

2. Piece of aluminium

3. Iron nail

4. Piece of coal

5. Lump of sulfur (pea-
sized)

6. Block of wood

Page 6 of 46

Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

Table 4.1: Appearance, hardness, and effect of hammering on different objects or materials
(blank, as printed on page 43).

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

S.NO. OBJECT/MATERIAL EFFECT OF HAMMERING WHAT THIS TELLS US

1. Piece of copper Flattens Malleable

2. Piece of aluminium Flattens Malleable

3. Iron nail Flattens Malleable

4. Piece of coal Breaks into pieces Brittle

5. Lump of sulfur (pea-sized) Breaks into pieces Brittle

6. Block of wood Neither flattens nor breaks Neither malleable nor brittle

Why it happens: in a metal the particles can slide over one another and settle in a
new position, so the piece simply spreads and gets thinner. In coal and sulfur the
particles cannot slide; the blow travels as a crack and the lump splits.

Caution: do this only under your teacher's or an adult's supervision, hold the
hammer with a firm grip, and keep your other hand well away from the striking
point.

In-text Questions — Page 43

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Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

Section 4.1.1 Malleability

IN-TEXT

Q1 Analyse Table 4.1. Identify the objects that are lustrous in appearance and hard.

S.NO. OBJECT/MATERIAL APPEARANCE HARD/SOFT EFFECT OF
(LUSTROUS/NON- HAMMERING
LUSTROUS) (FLATTENS/BREAK
INTO PIECES)

1. Piece of copper

2. Piece of aluminium

3. Iron nail

4. Piece of coal

5. Lump of sulfur (pea-
sized)

6. Block of wood

Table 4.1: Appearance, hardness, and effect of hammering on different objects or materials
(blank, as printed on page 43).

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

Lustrous + hard → copper, aluminium, iron → these are metals

Non-lustrous + not so hard → coal, sulfur, wood

The shine that copper, aluminium and iron show is given a special name — metallic lustre.

Why it happens: the surface of a metal reflects light evenly, so it gleams. Coal and
sulfur scatter light in all directions, so they look dull however much you polish them.

Page 8 of 46

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Class 7 Science Chapter 4 The World of Metals and Non-metals
g l AglaSem · NCERT Solutions

co m
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Are all metals hard and solid?
e
Q2

m l as
.co a g
a
s em
a l and solid” is the general rule for metals, not a law without exceptions.
No.g“Hard

Sodium and potassium are metals, yet they are so soft that they can be cut with a knife,
like a piece of cheese.
. com ag
a s em temperature — you have seen it in the
Mercury is a metal that is a liquid at room

agl
thermometers of the chapter ‘Temperature and its Measurement’ of Grade 6 Curiosity.

c om
Tip: in science, learn the general property first, then learn the famous exception. For
.
s
metals the two exceptions worth remembering are: softest — sodium
e mand
. comliquid — mercury.
potassium;
a gla
a s em
a gl
m a s
agl
Which objects did you find become flat on beating with a hammer?

.co
Q3

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g l a
a

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

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Beaten into a thin sheet without breaking = malleability
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g of all.
.c metals are malleable; gold and silver are the most malleable
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Most

agl Everyday proof of malleability is all around you — the thin silver foil (vark) on sweets and the
se m
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aluminium foil used to wrap food are both metals beaten into sheets.
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gl ase
Q4
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Can you give some examples of metal sheets?

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o m l a se
.cSilver vark on barfi and other sweets — silver beaten untilagit is thinner than paper.
m Aluminium foil for wrapping rotis and packing food.
l a se
ag Copper sheets beaten into tawas, parats and temple roofing.
.c
s e m
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Galvanised iron sheets used for roofs, buckets and trunks.

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Gold leaf used on idols and in traditional decoration.
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com
m .
m ase
.co


a g l Page 9 of 46

Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

Did you know? Gold can be beaten into a sheet so thin that light passes through it
with a greenish tinge. That is malleability pushed to its limit.

Holistic Lens — Page 44
The impact of iron on the progress of civilisation of India

HOLISTIC LENS

Q1 What could be the potential reason that it is generally considered that copper was
discovered earlier as compared to iron?

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

1. Copper is found in a nearly pure form in nature. Lumps of native copper can simply be
picked up, and their reddish metallic shine makes them easy to notice. Iron is almost always
locked up inside dull-looking rock (ore) that looks like ordinary stone.
2. Copper is easier to extract and melt. It can be got out of its ore and melted in a simple
wood or charcoal fire. Iron needs a much hotter furnace, with a way of blowing air in — a
technology that took people a long time to invent.
3. Copper is softer. It can be hammered into a pot or an ornament even when cold. Iron must
be heated red hot before it will take a shape, exactly as Sudarshan uncle does.

Why it matters: once the hotter furnace was mastered, iron changed life in India.
Iron ploughshares cut heavier soils than wooden or copper ones, harvests grew, and
settled farming villages could support towns. The Harappans used copper and gold,
but iron came into everyday use only much later.

In-text Questions — Pages 44 & 45

Page 10 of 46

Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

Sections 4.1.2 Ductility and 4.1.3 Sonority

IN-TEXT

Q1 Where do you find the use of metal wires?

WHERE YOU SEE METAL WIRE WHICH METAL, AND WHY IT IS USED

Electrical fittings in the house Copper or aluminium — good conductors of electricity

Ornaments — bangles, necklaces, earrings Gold, silver — very ductile, so they can be drawn fine and
twisted

Stringed instruments — veena, sitar, violin, Steel, brass — a taut metal wire vibrates and gives a clear note
guitar

A tea strainer, a sieve, wire mesh Steel wire woven into a net

Ropes of suspension bridges and cranes Steel wire, which can bear very heavy loads

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

Did you know? Gold is so ductile that one gram of it can be drawn into a 2
kilometre-long wire.

Q2 Have you ever seen wires made of coal or sulfur?

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

Pull a copper rod → it stretches thinner and thinner → ductile

Pull a stick of coal or sulfur → it snaps at once → not ductile

Page 11 of 46

Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

Why it happens: to become a wire, a material must be able to stretch without
breaking. In a metal the particles slide past one another and stay joined. In coal and
sulfur they cannot slide, so the piece cracks the moment it is pulled. Coal and sulfur
are non-metals, and non-metals are neither malleable nor ductile.

Q3 Have you ever noticed the sound produced when a metal spoon, or a metal plate, or
a metal coin is dropped on the floor? How is it different from the sound produced
when a piece of coal or wood is dropped on the floor?

The difference is easy to hear.

OBJECT DROPPED SOUND PRODUCED HOW LONG IT LASTS

Metal spoon, metal plate, coin A clear ringing sound Rings on for a moment after the fall

Piece of coal, block of wood A dull thud Stops the instant it lands

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

Why it happens: when a metal is struck it keeps vibrating for a while, and those
vibrations reach your ear as a long, clear note. Coal and wood stop vibrating almost
immediately, so you hear only a short, dull thud.

Did you know? The ring of the school bell and the jingle of ghungroos are both the
sonority of metals at work.

Activity 4.2: Let us investigate — Page 45

Page 12 of 46

Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

Section 4.1.3 Sonority

ACTIVITY

Q1 Take a few objects, such as a metal spoon, a coin, a piece of coal, and a block of
wood. Drop them one by one from a certain height. Do you notice any difference in
the sound produced by these objects?

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

OBJECT MATERIAL SOUND PRODUCED SONOROUS?

Metal spoon Steel Ringing Yes

Coin Metal alloy Ringing Yes

Piece of coal Carbon (non-metal) Dull thud No

Block of wood Wood Dull thud No

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

Did you know? A person who cannot see uses exactly this difference. As the white
cane taps the ground, a ringing tap means metal — a manhole cover or a grill — and
a dull tap means wood or stone. The sound draws the map of the path.

Caution: be careful while dropping the objects, and make sure no one's feet are
below.

In-text Questions — Page 46
Section 4.1.4 Conduction of heat

IN-TEXT

Q1 Have you ever observed the vessels used for cooking in the kitchen?

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.

Page 13 of 46

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Class 7 Science Chapter 4 The World of Metals and Non-metals
g l AglaSem · NCERT Solutions

The tawa, kadhai, pressure cooker and patila are made of aluminium, steel, iron or copper.
co m
Their handles are wood, bakelite or plastic, or the metal handle is wrapped in cloth.
em.
m l as
.co a g
a s em
Why it happens: the vessel must let heat pass from the flame into the food quickly,
gl it is made of a metal — a good conductor of heat. The handle must stop heat
aso
from reaching your fingers, so it is made of a poor conductor.

co m
m . ag
l a se
Q2 agthat are used for making cooking vessels?
Can you name some metals

co m
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METAL .co
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WHERE YOU SEE IT IN THE ag THE JOB
WHY IT SUITS

a s
agl
KITCHEN

Aluminium Pressure cooker, patila, tawa Very good conductor, light, cheap

m a s
Iron Kadhai, tawa
em
.co Strong, stands high heat, spreads heat evenly
agl
a s
Copper
agl bhagona
Base of steel vessels, The best conductor of heat among common
metals

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Steel (iron + Most modern vessels
m .
Good conductor and does not rust easily
carbon)
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s m
eTip:
gl a look at the bottom of a good steel patila — many have a copper or aluminium
a disc fixed there. Steel alone conducts heat rather slowly, so a better conductor is
se m
added exactly where the flame touches.
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Do you know why these metals are used for this purpose?
Q3

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Because

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Flame heats the base of the vessel
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Heat travels through the metal by conduction
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Heat reaches the food and cooks it — quickly and evenly
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A vessel of wood or clay would be far slower, and wood would simply burn.

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Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

Why it happens: in a metal, heat is passed on rapidly from particle to particle right
through the piece, so the whole vessel becomes hot in seconds. In wood, plastic or
clay this passing on is very slow, which is why the same materials are chosen for
handles.

Activity 4.3: Let us investigate — Pages 46 & 47
Section 4.1.4 Conduction of heat

ACTIVITY

Q1 Which of the spoons get hotter?

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

SPOON UPPER END AFTER A FEW MINUTES CONCLUSION

Metal spoon Distinctly hot to touch Metal is a good conductor of heat

Wooden spoon Barely warm Wood is a poor conductor of heat

HOT barely warm

hot water

Metal spoon Wooden spoon

Page 15 of 46

Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

Both spoons stand in the same hot water for the same time, yet only the metal one carries the heat
up to your fingers.

Caution: perform this only under the supervision of your teacher or an adult, and be
careful while handling hot water.

Q2 What does this experiment tell us about heat transfer along the two spoons?

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.

Transfer of heat from one point of a material to another = conduction

Materials that transfer heat = conductors

Metals → good conductors of heat. Wood → poor conductor of heat.

Why it happens: the only difference between the two spoons was the material —
the size, thickness, water and time were all kept the same. So the difference in the
result must come from the material itself. This is what makes it a fair experiment.

Tip: this is why metal cooking vessels are given wooden or plastic handles, and why
you will meet this idea again in the chapter ‘Heat Transfer in Nature’.

In-text Questions — Page 47
Section 4.1.5 Conduction of electricity

IN-TEXT

Q1 Have you ever seen an electrician using a screwdriver? What type of material is
used for making its handle?

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

Page 16 of 46

Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

Steel rod → good conductor → does the work at the screw

Plastic handle → poor conductor of electricity → protects the hand

Why it happens: if the electrician's screwdriver touches a live wire, electricity could
travel up the steel rod. The plastic covering does not let electricity pass into the
hand, so the current cannot complete a path through the body and no shock is felt.

Q2 You may have also noticed the electrician wearing rubber gloves and shoes while
working. What can be the reason for this?

Rubber is a poor conductor of electricity, so gloves and shoes of rubber keep the electrician
out of the electric circuit.
For a person to get a shock, electricity must find a complete path — from the live wire, through
the body, to the ground. Rubber blocks that path at both ends:

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

Check it yourself: notice how a lineman also works on a wooden ladder, not a metal
one. Wood, like rubber and plastic, is a poor conductor.

Activity 4.4: Let us design and create — Pages 47 & 48

Page 17 of 46

Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

Section 4.1.5 Conduction of electricity

ACTIVITY

Q1 Design an electric circuit, like the ‘tester’ circuit in the chapter ‘Electricity: Circuits
and their Components’. Repeat the same activity using the materials listed below
and record your observations in Table 4.2.

S.NO. OBJECT/MATERIAL OBSERVATION GOOD CONDUCTOR OF
(BULB ELECTRICITY OR POOR
GLOWS/DOES NOT CONDUCTOR OF
GLOW) ELECTRICITY

1. Piece of aluminium
foil

2. Iron nail

3. Lump of sulfur (pea-
sized)

4. …

Table 4.2: Conduction of electricity by different objects or materials (blank, as printed on
page 48).

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.

Page 18 of 46

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Class 7 Science Chapter 4 The World of Metals and Non-metals
g l AglaSem · NCERT Solutions

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?

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The tester: the object being tested is placed in the gap. A glowing bulb meanseelectricity
s
co m gl a
. through it.
a
a sem
agl Tip: scrape the surface of an old nail or a coal piece clean before testing. A dirty or

m a s
.co agl
coated surface can stop contact and give you a wrong “does not glow”.

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Q2 Predict which of these could make the bulb of the tester glow and which could not.

c o m
(Objects: a piece of aluminium foil, an iron nail, a lump of sulfur (pea-sized), a
.
m made of rubber
s e
copper wire, a piece of coal, a piece of dry wood, a stone, an eraser

. oma piece of nylon rope.)
cand a gla
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aANSWER
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Write the prediction first, then test. A completed Table 4.2 looks like this.
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m ase
.co


a g l Page 19 of 46

Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

S.NO. OBJECT/MATERIAL OBSERVATION (BULB GOOD OR POOR
GLOWS/DOES NOT GLOW) CONDUCTOR OF
ELECTRICITY

1. Piece of aluminium foil Glows Good conductor

2. Iron nail Glows Good conductor

3. Lump of sulfur (pea- Does not glow Poor conductor
sized)

4. Copper wire Glows Good conductor

5. Piece of coal Does not glow Poor conductor

6. Piece of dry wood Does not glow Poor conductor

7. Stone Does not glow Poor conductor

8. Eraser made of rubber Does not glow Poor conductor

9. Piece of nylon rope Does not glow Poor conductor

Q3 Do you see any pattern in the glowing of bulbs when using different materials in
Activity 4.4?

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

Aluminium, iron, copper → bulb glows → metals
Sulfur, coal, wood, stone, rubber, nylon → bulb does not glow → non-metals and other

materials

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.

Why it matters: this single pattern explains the electrician's kit. The wires are metal
so that current flows, and the screwdriver grip, gloves and shoes are plastic and
rubber so that current cannot flow into the body.

Page 20 of 46

Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

In-text Questions — Page 48
Section 4.2 Effect of Air and Water on Metals: Iron

IN-TEXT

Q1 You would have often noticed that iron objects develop brown deposits when left in
the open for a few days. In which conditions would an iron object develop brown
deposits?❖ When it comes into contact with dry air only. ❖ When it comes into
contact with water only. ❖ When it comes into contact with both air and water.

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

Dry air only → no brown deposit

Water only (no dissolved air) → no brown deposit

Air and water together → brown deposit forms

Do not accept this as a guess — Activity 4.5 sets up exactly these three conditions in three
bottles and lets you see the answer for yourself over 8 – 10 days.

Check it yourself: look at an iron gate in your locality. The worst rusting is always at
the bottom edge, where rainwater collects and air is still available — not on a dry
sheltered part.

Activity 4.5: Let us experiment — Pages 49 & 50

Page 21 of 46

Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

Section 4.2 Effect of Air and Water on Metals: Iron

ACTIVITY

Q1 Place all the glass bottles undisturbed at room temperature and observe the
changes for 8 – 10 days. Record your observations in Table 4.3.

A Thread B Thread C Thread

Oil
Iron nail
Iron nail Iron nail
Silica gel
Water Water

Fig. 4.4(a) Fig. 4.4(b) Fig. 4.4(c)

Fig. 4.4, page 49: Glass bottles containing iron nails.

GLASS CONDITIONS OBSERVATIONS
BOTTLE
PRESENCE OF WATER PRESENCE OF AIR
(YES/NO) (YES/NO)

A No Yes

B

C

Table 4.3: Formation of brown deposit on iron nails (page 49; row A is pre-filled in the
book).

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

Page 22 of 46

Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

GLASS WHAT IS INSIDE PRESENCE OF PRESENCE OF OBSERVATIONS
BOTTLE WATER AIR (YES/NO)
(YES/NO)

A Iron nail + silica gel, No Yes No brown deposit — the
capped tightly nail stays shining

B Iron nail fully dipped Yes No No brown deposit — the
in boiled and cooled nail stays shining
water, oil layer on
top, capped

C Iron nail partly Yes Yes Brown deposit appears,
dipped in water, mostly near the water line
bottle left open

A: dry air B: water, no air C: air + water
no rust no rust rust forms
Bottle A is capped with silica gel (dry air), bottle B has boiled water sealed under an oil layer (no air),
bottle C is open with the nail half in water.

Tip: the silica gel in bottle A soaks up moisture, the boiling drives dissolved gases
out of the water in bottle B, and the oil layer stops fresh air from dissolving back in.
Each step removes exactly one thing — that is what makes the experiment a fair
test.

Page 23 of 46

as e
a
Class 7 Science Chapter 4 The World of Metals and Non-metals
g l AglaSem · NCERT Solutions

co m
m.
What can you conclude from this experiment?
e
Q2

m l as
.co a g
a s em
a gl
Conclusion: the presence of both water and air is essential for brown deposits to develop
on iron.

com
m . ag
Bottle A (air only, dry) → no deposit
l a se
agdeposit
Bottle B (water only, no air) → no

Bottle C (air and water) → brown deposit
co m
em.
m as
So moist air is responsible for the brown deposit on iron objects.

.co a g l
se m
g l a
This brown deposit is called rust, and the process of its formation on objects made of iron is
a called rusting.
m a s
.co
Why it happens: rusting is a slow reaction between iron, the oxygen of the air and
m agl
l a se
water. Take away either one and the reaction cannot start — which is exactly what
bottles A and B prove. a g

co m
Did you know? Rusting is not limited to iron. Copper objects grow a green coating
m .
m as e
c o g l
and silver objects a black one. The general name for this gradual eating away of a
. surface by air, water or other substances is corrosion.
a
e m
as
metal

agl
se m
com g l a
In-text Questions — Page 50
m . a
ase
agl
Section 4.2 — Corrosion

IN-TEXT

co m
m .
Q1
mor a black coating on the surface of silver objects? glas e
Have you noticed the formation of a green coating on the surface of copper objects

. c o a
a s em
agl ANSWER
.c
Yes — an old copper lota left unused grows a dull green layer, and silver jewellery or a silver
s e m
m a
. co agl
spoon slowly turns black.

e m
g l as
a

com
m .
m ase
.co


a g l Page 24 of 46

Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

METAL COATING THAT FORMS IN THE OPEN NAME OF THE PROCESS

Iron Brown deposit (rust) Rusting — a kind of corrosion

Copper Green coating Corrosion

Silver Black coating Corrosion

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

Why it matters: rusting is a serious problem for the country. Every year an
enormous amount of money is spent to replace or repair iron structures — bridges,
railway tracks, gates, pipes — damaged by rust. It is prevented by painting, oiling,
greasing and galvanisation (a protective layer of zinc on the iron).

Did you know? The Iron Pillar of Delhi, made in the time of Chandragupta II more
than 1600 years ago, is about 8 metres high and weighs more than 6000 kilograms
— and after all those centuries of wind and rain it has barely any rust. It was made in
a way that resists rusting, and it shows how advanced metal technology already was
in India.

Activity 4.6: Let us investigate (demonstration activity) — Page 51
Section 4.3 Effect of Air and Water on Other Metals

ACTIVITY

Q1 Let the magnesium ribbon burn. What do you observe?

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

Magnesium + oxygen (of the air) on burning → magnesium oxide

Silvery ribbon → blinding white light → white powder

Page 25 of 46

Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

Why it happens: magnesium reacts with the oxygen present in the air. So much
energy is released that the light is painfully bright, and the new substance formed —
magnesium oxide — is a white powder quite unlike the shiny grey ribbon you started
with.

Caution: this is a demonstration activity, done by the teacher. Wear protective
eyeglasses, keep a safe distance and never look straight at the flame — the light can
hurt the eyes. Clean the ribbon with sandpaper first, and hold it with a pair of tongs.

Q2 Recall the chapter ‘Exploring Substances: Acidic, Basic, and Neutral’. Find out
whether the solution of magnesium oxide is acidic or basic or neutral in nature. You
can use any acid-base indicator.

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

INDICATOR USED WHAT YOU SEE WHAT IT MEANS

Red litmus paper Turns blue Basic

Blue litmus paper Stays blue (no change) Not acidic

Turmeric (haldi) paper Turns reddish-brown Basic

China rose indicator Turns green Basic

Generally, oxides of metals are basic in nature.

Tip: use warm water — magnesium oxide dissolves very little in cold water, and a
weak solution may not change the indicator clearly.

Page 26 of 46

Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

Q3 What effect does this solution have on blue and red litmus papers?

Red litmus paper → turns blue

Blue litmus paper → no change, stays blue

Therefore the solution of magnesium oxide is 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.

Why it matters: this one test result stands for a whole family. Magnesium is a
metal, its oxide dissolves to give a basic solution, and the same is true for metals in
general — metal oxides are basic. You will meet this burning of magnesium again
in the chapter ‘Changes Around Us: Physical and Chemical’.

In-text Questions — Page 52
Section 4.3 — Sodium

IN-TEXT

Q1 Do you know that sodium is a metal which is stored in kerosene because it reacts
vigorously with oxygen and water. A lot of heat is generated in the reaction. Storing
sodium in kerosene prevents its exposure to moisture and air. Can you predict the
nature of its oxide?

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

Sodium (a metal) + oxygen → sodium oxide

Sodium oxide + water → a solution that turns red litmus blue

So the oxide of sodium is basic.

Page 27 of 46

Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

Why it happens: you have just seen magnesium — a metal — give a basic oxide.
The rule holds for metals generally, so without doing any experiment you can predict
the answer for sodium. This is how a scientific generalisation is used: prove it once
carefully, then apply it.

Caution: never handle sodium yourself. It reacts so violently with the moisture of
the air and with water that it catches fire — which is exactly why it is kept under
kerosene, where neither air nor water can reach it.

Activity 4.7: Let us experiment (demonstration activity) — Pages 52 & 53
Section 4.4 Substances that Behave Differently from Metals in Air and Water

ACTIVITY

Q1 Again, recall the chapter ‘Exploring Substances: Acidic, Basic, and Neutral’. Using an
acid-base indicator, check whether the solution obtained after the addition of water
to the gas jar is acidic or basic or neutral.

Burn a little powdered sulfur in a deflagrating spoon, lower it into a gas jar, cover the jar, then
after 3 – 4 minutes add a small quantity of water, replace the lid and shake so that the gas
dissolves. Test that solution.

INDICATOR USED WHAT YOU SEE WHAT IT MEANS

Blue litmus paper Turns red Acidic

Red litmus paper Stays red (no change) Not basic

China rose indicator Turns dark pink Acidic

Caution: this is a demonstration activity for the teacher, and it must be performed in
a fume hood or a well-ventilated area. Burning sulfur produces gases which can be
harmful if inhaled.

Page 28 of 46

as e
a
Class 7 Science Chapter 4 The World of Metals and Non-metals
g l AglaSem · NCERT Solutions

co m
m.
What do you observe?
e
Q2

m l as
.co a g
a
s em
a l
Yougobserve that the solution is acidic in nature — it turns blue litmus red.

co m
. ag
Sulfur + oxygen (air) on burning → sulfur dioxide gas
em
Sulfur dioxide + water → sulfurous acid
g l as
a
So the oxide of a non-metal gives an acidic solution.

co m
se m.
o m l a
Why it matters: place this beside Activity 4.6 and the whole chapter falls into place.
g an acidic oxide. The
m .c (metal) gave a basic oxide; sulfur (non-metal) gives a
se
Magnesium

g l a
behaviour of an element's oxide is one of the surest ways of telling a metal from a
a non-metal.

om a s
e
. c
mhappens in the open air when fuels containing agl
Did you know? The same reaction
a s
agl dissolves in rain and falls as acid rain, which
sulfur are burnt. The sulfur dioxide
damages crops, buildings and statues.

co m
m .
o m l a se
.c 4.8: Let us explore — Page 53 a g
m
se 4.4 Substances that Behave Differently from Metals in Air and Water
Activity
l a
ag
Section

ACTIVITY
se m
com g l a
m . a
ase
agl
Q1 Does sulfur behave in water the same way metals do?

m

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

m l as
.co g
at all.

em SUBSTANCE a
a s
gl
KEPT IN WATER AND AIR FOR DAYS RESULT
a c
m .
s e
Iron (metal) Nail half dipped in water, bottle open Brown deposit — rust forms

m a
m . co agl
se
Sulfur (non-metal) Powder added to water in a tumbler No reaction at all

l a
g not react with water.
Generally, non-metals a
do

com
m .
m ase
.co


a g l Page 29 of 46

Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

Q2 Take some sulfur powder in a glass tumbler. Add a small amount of water to it.
What do you observe?

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.

Sulfur + water → no change
Non-metals generally do not react with water.

Why it matters: this is the point of the whole section. Sulfur and phosphorus
behave differently from metals with air and water. They are usually soft and dull in
appearance, neither malleable nor ductile, not sonorous and poor conductors of
heat and electricity. Such substances are called non-metals, and their oxides are
acidic.

Did you know? Not every non-metal ignores water. Phosphorus is stored in water,
because it catches fire the moment it is exposed to atmospheric air — the exact
opposite of sodium, which is a metal kept in kerosene to keep water away from it.

In-text Questions — Page 54
Section 4.5 Are Non-metals Essential in Everyday Life?

IN-TEXT

Q1 We breathe in oxygen, which is a non-metal, and without it, we would not be able to
survive. Can you think of any other uses of oxygen?

Oxygen cylinders in hospitals for patients who cannot breathe enough on their own.
Mountaineers and deep-sea divers carry oxygen cylinders where the air is thin or absent.
Burning — no fuel can burn without oxygen. Coal in the ironsmith's furnace, gas on the
kitchen stove and wood in a chulha all need it.
Cutting and welding metals — an oxygen flame is hot enough to melt steel.
Aquatic life — fish use the oxygen dissolved in water, which is why an aquarium needs an air
pump.

Page 30 of 46

Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

Rockets carry liquid oxygen with them, because there is no air in space to burn the fuel.

Did you know? The other non-metals are just as useful: carbon is the building block
of all life forms and a key part of proteins, fats and carbohydrates; nitrogen goes
into fertilisers; chlorine purifies water; and a solution of iodine is applied on
wounds as an antiseptic.

Let Us Enhance Our Learning — Pages 55 & 56
End-of-chapter exercise

LET US ENHANCE OUR LEARNING

Q1 Which metal is commonly used to make food packaging materials as it is cheaper,
and its thin sheets can be folded easily into any shape? (i) Aluminium (ii) Copper (iii)
Iron (iv) Gold

(i) Aluminium

OPTION WHY IT IS OR IS NOT THE ANSWER

(i) Aluminium Correct — cheap, light, highly malleable, does not rust, safe with food

(ii) Copper Costlier, and its surface forms a green coating that is not safe for food packing

(iii) Iron Heavy, and it rusts in moist air

(iv) Gold The most malleable, but far too expensive for wrapping food

Why it happens: the question gives two clues — “cheaper” and “thin sheets folded
easily”. Only a metal that is both inexpensive and very malleable fits, and that is
aluminium. This is the foil you see around chocolates, medicines and packed food.

Q2 Which of the following metal catches fire when it comes in contact with water? (i)
Copper (ii) Aluminium (iii) Zinc (iv) Sodium

(iv) Sodium

Page 31 of 46

Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

Sodium + water → vigorous reaction + a lot of heat → the metal catches fire

That is why sodium is stored in kerosene.

Why it happens: sodium reacts with oxygen and water so violently that the heat
produced is enough to set it alight. Kerosene keeps both moisture and air away from
it. Copper, aluminium and zinc do not react with water in this way.

Tip: do not confuse this with phosphorus, which is a non-metal and is stored in
water because it catches fire in air. Sodium: metal, kept in kerosene. Phosphorus:
non-metal, kept in water.

Q3 State with reason(s) whether the following statements are True [T] or False [F]. (i)
Aluminium and copper are examples of non-metals used for making utensils and
statues. [ ] (ii) Metals form oxides when combined with oxygen, the solution of
which turns blue litmus paper to red. [ ] (iii) Oxygen is a non-metal essential for
respiration. [ ] (iv) Copper vessels are used for boiling water because they are good
conductors of electricity. [ ]

STATEMENT T/F REASON

(i) Aluminium and copper are False Aluminium and copper are metals, not non-metals. They
examples of non-metals used for are lustrous, hard, malleable, ductile and good
making utensils and statues. conductors. The uses stated are correct, only the word
“non-metals” is wrong.

(ii) Metals form oxides when False Metal oxides are basic, so their solution turns red litmus
combined with oxygen, the solution of blue. Turning blue litmus red is the behaviour of an acidic
which turns blue litmus paper to red. solution, which is what a non-metal oxide such as sulfur
dioxide gives.

(iii) Oxygen is a non-metal essential True Oxygen is a non-metal, and we breathe it in. Without it we
for respiration. would not survive.

(iv) Copper vessels are used for False The reason is wrong. Copper is chosen because it is a
boiling water because they are good good conductor of heat, so heat passes quickly from the
conductors of electricity. flame into the water. Its electrical conductivity has nothing
to do with boiling water.

Page 32 of 46

Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

Tip: in a True/False question, always check the reason as carefully as the fact.
Statement (iv) is a true fact joined to a wrong reason — and that makes the whole
statement false.

Q4 Why are only a few metals suitable for making jewellery?

Jewellery makes an unusual set of demands, and only a handful of metals — mainly gold, silver
and platinum — meet all of them.

1. They must not corrode. Jewellery is worn every day against sweat and in moist air. Gold and
silver resist corrosion, so they keep their shine for generations. Iron would rust and copper
would grow a green coating.
2. They must be highly malleable and ductile. A necklace or an earring needs the metal to be
drawn into fine wire and beaten into delicate shapes. Gold is the most malleable and most
ductile of all metals — one gram can be drawn into a 2 kilometre-long wire.
3. They must be soft enough to work, yet lasting. Gold and silver can be shaped by a
goldsmith with simple tools, unlike iron which needs a furnace.
4. They must be lustrous and attractive. The yellow shine of gold and the white shine of
silver do not fade.
5. They must be safe on the skin. These metals do not harm the body.
6. They are rare. Rarity gives them value, which is why jewellery is also a family's savings.

Why it happens: most metals fail on the very first point. Ordinary metals react
slowly with air and moisture, and a corroded ornament loses both its beauty and its
worth.

Q5 Match the uses of metals and non-metals given in Column I with the jumbled
names of metals and non-metals given in Column II. Column I: (i) Used in electrical
wiring (ii) Most malleable and ductile (iii) Living organisms cannot survive without
it. (iv) Plants grow healthy when fertilisers containing it are added to the soil. (v)
Used in water purification. Column II: (a) E N X Y G O (b) N E C O H I R L (c) P E P O R C
(d) T E N G O I N R (e) O G D L

First unjumble Column II, then match.

Page 33 of 46

as e
a
Class 7 Science Chapter 4 The World of Metals and Non-metals
g l AglaSem · NCERT Solutions

co m
m.
COLUMN II ( JUMBLED) UNJUMBLED NAME METAL OR NON-METAL

m as e
(a) E N X Y G O
.co
OXYGEN
a
Non-metal
g l
se m
g l a Non-metal
a
(b) N E C O H I R L CHLORINE

(c) P E P O R C COPPER Metal

co m
(d) T E N G O I N R NITROGEN
e m . Non-metal ag
g l as
(e) O G D L
aGOLD Metal

co m
m.
COLUMN I MATCHES ANSWER REASON

m as e
.co
(i) Used in electrical wiring (c) Copper
a g l
An excellent conductor of electricity

a s em and ductile enough to be drawn into

ag l wire

s
The most malleable and most ductile
a
(ii) Most malleable and ductile (e) Gold
m
.co agl
of all metals

se m
(iii) Living organisms cannot survive
g l a
(a) Oxygen Needed for respiration
without it. a

co m
Used in making fertilisers; an essential
.
(iv) Plants grow healthy when (d) Nitrogen
fertilisers containing it are added to
e m
nutrient for plant growth

m l as
.co g
the soil.

m a
l a se
(v) Used in water purification (b) Chlorine Commonly used to purify drinking

a g water

se m
co(v)m– (b) g l a
. a
em
(i) – (c), (ii) – (e), (iii) – (a), (iv) – (d),
a s
agl

co m
Q6 What happens when oxygen reacts with magnesium and sulfur. What are the main
m .
as e
com
differences in the nature of products formed?

. a g l
e m
as
agl

Both burn in oxygen and both form an oxide — but one oxide is basic and the other is
.c
s e m
m a
acidic.

e m . co agl
g l as
a

co m
m .
m as e
.co


a g l Page 34 of 46

Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

Magnesium + oxygen → magnesium oxide (a white powder)

Magnesium oxide + water → a solution that turns red litmus blue → basic

Sulfur + oxygen → sulfur dioxide (a gas)

Sulfur dioxide + water → sulfurous acid, which turns blue litmus red → acidic

POINT OF MAGNESIUM (A METAL) SULFUR (A NON-METAL)
DIFFERENCE

How it burns With a dazzling white flame With a pale blue flame, giving off a
choking gas

Product formed Magnesium oxide — a white solid Sulfur dioxide — a gas
powder

Nature of the solution in Basic Acidic
water

Effect on litmus Red litmus → blue Blue litmus → red

Why it matters: this is the general rule of the chapter — metal oxides are basic,
non-metal oxides are acidic. Testing an element's oxide with litmus is therefore a
reliable way of deciding whether the element is a metal or a non-metal.

Page 35 of 46

Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

Q7 Complete the following flow chart:

? + Air + Heat Ash

Water

?

Add blue and red litmus
solutions separately

Change in blue Change in red
litmus solution litmus solution

? Blue

The flow chart printed with question 7 on page 56.

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.

Magnesium + Air + Heat Ash

Water

Magnesium oxide
solution (basic)

Add blue and red litmus
solutions separately

Change in blue Change in red
litmus solution litmus solution

No change (stays blue) Blue

The completed flow chart. The three purple boxes are the ones you have to fill in.

Page 36 of 46

Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

BOX MARKED “?” ANSWER REASON

First box (burnt in air Magnesium (a metal) Burning magnesium ribbon in air gives a
with heat) white ash

Ash + water Magnesium oxide solution — a The ash is magnesium oxide; metal oxides
basic solution give basic solutions

Change in blue litmus No change — it remains blue A basic solution does not change blue litmus
solution

Tip: the filled-in “Blue” at the bottom right is the key to the whole chart. Red litmus
turning blue can only mean a base, and only a metal oxide is basic.

Q8 You are provided with the following materials. Discuss which material would be
your choice to make a pan that is most suitable for boiling water and why? Iron,
copper, sulfur, coal, plastic, wood, cardboard

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

MATERIAL SUITABLE? REASON

Copper Best choice Metal — the best conductor of heat here, so water boils fast; malleable,
so it can be beaten into a pan; hard, strong and does not melt or burn

Iron Also suitable A good conductor and very strong, but heavier and it rusts if left wet

Sulfur No Non-metal — brittle, cannot be shaped into a pan, poor conductor, and
it burns

Coal No Brittle, poor conductor — and it is a fuel, so it would burn

Plastic No Poor conductor of heat and it melts on a flame

Wood No Poor conductor and it catches fire

Cardboard No Poor conductor, soaks up water and burns at once

Page 37 of 46

Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

Why it happens: a pan for boiling water must do three things — carry heat quickly
from the flame into the water, hold its shape when hot, and not catch fire or melt.
Only a metal does all three, and among the metals offered copper conducts heat
best.

Tip: the handle should not be copper. Fit a wooden or plastic handle, because a poor
conductor there keeps your hand safe.

Q9 You are provided with three iron nails, each dipped in oil, water and vinegar. Which
iron nail will not rust, and why?

The nail dipped in oil will not rust.

NAIL WILL IT WHY
DIPPED IN RUST?

Oil No Oil does not contain water and does not let air dissolve into it, so the
nail is cut off from both air and moisture. Oiling is in fact one of the
standard ways of preventing rust.

Water Yes Ordinary water has air dissolved in it, so both air and water reach the
nail

Vinegar Yes — fastest Vinegar is an acid solution in water, and acid speeds up the eating
of the three away of the iron surface

Rusting needs air + water together

Oil supplies neither → no rusting

Why it happens: a film of oil acts as a physical barrier. This is exactly why cycle
chains, tools and machine parts are oiled or greased, and why your grandmother
rubs a little oil on the tawa before putting it away.

Page 38 of 46

as e
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Class 7 Science Chapter 4 The World of Metals and Non-metals
g l AglaSem · NCERT Solutions

co m
m.
How do the different properties of metals and non-metals determine their uses in
e
Q10

m l as
.co
everyday life?

a g
se m
g l a
a

A material is chosen for a job because of the property the job demands. Change the

m
property and the use changes with it.
. co ag
m
e USE IT LEADS TO
PROPERTY WHO HAS IT
g l as
Malleability Metals
a Aluminium foil, silver vark, tawas and buckets beaten out of

com
sheets

.
a s emtea strainers, chains
com agl
Ductility Metals Electrical wires, sitar and veena strings,

m . and ornaments

e
as conductor of
a g lGood Metals Cooking vessels, pressure cookers, kadhais
heat

m of pans and ladles a s
.co agl
Poor conductor of Wood, plastic Handles

se m
a
heat

Good conductor of Metals a g l Copper and aluminium wiring, switches, plug pins
electricity

co m
m .
as e
Poor conductor of Rubber, plastic (non- Wire insulation, screwdriver grips, electrician's gloves and

m l
.co g
electricity metallic materials) shoes

m
eSonority a
a s
gl
Metals School bells, temple bells, ghungroos, cymbals

a
se m
Hardness and Metals Farm tools, girders, railway lines, suspension bridge cables
strength
com g l a
m . a
ase
agl
Lustre and resistance Gold, silver Jewellery and coins
to corrosion

m
Non-metals

co
Chemical usefulness Oxygen for breathing, nitrogen for fertilisers, chlorine for

m .
water purification, iodine as an antiseptic, carbon as the

m
building block of life
as e
.co a g l
se m
g l a
a
Why it matters: look at any single object and you can read the science in it. A
screwdriver is metal where it must carry force and plastic where it must stop current;
.c
s e m
m a
agl
a kadhai is metal where it meets the flame and wood where it meets your hand.
. co
m
Nothing is chosen by accident.
as e
a g l

co m
m .
m as e
.co


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Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

Q11 One of the methods of protecting iron from getting rusted is to put a thin coating
of zinc metal over it. Since sulfur does not react with water, can it be used for this
purpose? Justify your answer.

No, sulfur cannot be used. Not reacting with water is only one of the things a protective
coating must do, and sulfur fails all the others.

1. Sulfur is brittle, not malleable or ductile. A coating has to be spread as a thin, continuous,
tightly stuck film. Sulfur is a soft, crumbly non-metal — it cannot be beaten or drawn into a
layer, and any layer would crack and flake off.
2. It will not stick to the iron. Zinc bonds firmly to the iron surface; loose sulfur powder
simply rubs away, leaving the iron bare again.
3. A cracked coating is worse than none. Once moist air reaches the iron through the gaps,
rusting starts there — and being trapped under the coating, it may go unnoticed until the
damage is done.
4. Zinc does more than merely cover. Even if a galvanised sheet is scratched, the zinc keeps
protecting the exposed iron. Sulfur offers no such protection at all.
5. Sulfur burns. A sulfur-coated iron object near a flame would burn and give off harmful
sulfur dioxide gas.

Why it happens: the argument in the question is a trap. “Sulfur does not react with
water” is true, but the question a scientist must ask is “can it form and hold a
protective layer?” — and there the answer is a clear no. The correct methods remain
painting, oiling, greasing and galvanisation.

Q12 An ironsmith heats iron before making tools. Why is heating necessary in this
process?

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.

1. Cold iron is hard and stiff. Hammering it wastes effort — the blows bounce off, and a heavy
blow may crack the piece instead of bending it.
2. Red hot iron is soft. Each hammer blow now spreads and bends the metal. Sudarshan uncle
heats the block until it is red hot and only then beats it into an axe.
3. The shape can be changed many times. The smith can flatten, curve, punch a hole and
draw out an edge, reheating whenever the piece cools and stiffens.
4. The tool comes out stronger. Shaping by hammering, rather than by cutting metal away,
leaves the iron dense and tough, so the edge of a kulhadi lasts.

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Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

Cold iron + hammer → resists, may crack

Heated (red hot) iron + hammer → flattens and bends into shape

Heating increases the malleability of iron.

Did you know? This craft is thousands of years old. The Iron Pillar of Delhi was
shaped by smiths working iron in exactly this way, and it still stands almost free of
rust after more than 1600 years.

Exploratory Projects — Page 56
Projects and further exploration

EXPLORATORY PROJECTS

Q1 Dhokra, Bidriware, Pembarthi, and Kamrupi are some of India’s famous metal art
styles. Find out the states where these artworks are made. Also, make a collage of
their photographs.

METAL STATE(S) METAL USED AND WHAT IT LOOKS LIKE
ART STYLE

Dhokra Chhattisgarh, Odisha, West Brass/bronze figures cast by the lost-wax method —
Bengal, Jharkhand (also parts of tribal figures, elephants, lamps, with fine thread-like
Telangana) lines on the surface

Bidriware Karnataka (Bidar) A blackened zinc-copper alloy inlaid with silver wire
— vases, boxes, hookah bases

Pembarthi Telangana (Pembarthi village, Sheet-brass work beaten into temple lamps, plates
Jangaon district) and panels — a direct use of malleability

Kamrupi Assam (Kamrup region, especially Bell-metal and brass utensils — xorai, bota, bowls
Hajo and Sarthebari) and plates

How to make the collage:

1. Collect four to six pictures for each style — from old magazines, newspapers, tourism
pamphlets, or printouts.
2. Divide a chart paper into four regions, one per style.
3. Paste the pictures and label each with the style name, the state and the metal used.

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Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

4. Draw a small outline map of India in a corner and mark the four regions with arrows to the
correct panel.
5. Add one line under each panel on the property of the metal the craft depends on —
malleability for Pembarthi sheet work, the ability of molten brass to fill a mould for Dhokra.

Q2 On a map of India, mark the states where iron, gold, aluminium and other metals
are found.

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

METAL ORE MINED CHIEF STATES

Iron Haematite, Odisha, Chhattisgarh, Jharkhand, Karnataka, Goa, Maharashtra
magnetite

Gold Gold ore Karnataka (Kolar, Hutti), Andhra Pradesh (Ramagiri), Jharkhand

Aluminium Bauxite Odisha, Gujarat, Jharkhand, Chhattisgarh, Maharashtra

Copper Copper ore Rajasthan (Khetri), Jharkhand (Singhbhum), Madhya Pradesh
(Malanjkhand)

Manganese Manganese ore Odisha, Karnataka, Madhya Pradesh, Maharashtra

Zinc and Zinc-lead ore Rajasthan (Zawar, Rampura Agucha)
lead

Tip: add a legend box in a corner of the map, and colour the state, not just a dot —
you will notice at once that a broad belt through Odisha, Jharkhand and
Chhattisgarh carries most of India's iron. That is why the country's big steel plants
stand there.

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Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

Q3 Explore the metals and non-metals found in smartphones and find out how they
help the phone work properly.

ELEMENT METAL OR NON- WHERE IT IS IN THE PHONE AND WHAT IT DOES
METAL

Copper Metal The wiring and the tracks on the circuit board — carries
electricity because it is a good conductor and very ductile

Gold Metal Thin plating on connectors and contacts — conducts well and
does not corrode, so the contact never goes bad

Aluminium Metal The body/frame — light, strong and carries heat away from
the chip

Lithium and Metals The rechargeable battery, which stores and supplies the
cobalt energy

Silver Metal Conducting pastes and switch contacts — the best conductor
of electricity of all

Silicon Behaves in between (a The processor and memory chips — the “brain” of the phone
semiconductor)

Carbon Non-metal The plastics of the case and the graphite in the battery
electrode

Oxygen (in Non-metal The screen glass, which is hard, transparent and does not
glass) conduct electricity

Why it matters: the phone works only because metals and non-metals are placed
exactly where their properties are needed — conductors to carry the current, non-
conductors to keep it from going where it should not, and a hard transparent non-
metallic glass in front of it all. Many of these metals are scarce, which is why old
phones should be given for recycling rather than thrown away.

Page 43 of 46

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Organise a classroom debate on whether the use of metals for comfort and luxury
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should be increased or decreased.

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no metal, but which use. Metal in a railway line, a bridge or a hospital serves everyone. Metal

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used only to show wealth serves no one and costs a forest. Our team therefore argues for

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se and aluminium are already recycled in large amounts, and every recycled tonne is a tonne
reducing

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There are exceptions to every rule — sodium and potassium are so soft they can be cut
with a knife, and mercury

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m as e
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a g l Page 44 of 46

Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

Metals are good conductors of heat and electricity. That is why cooking vessels are metal
while their handles are wood, and why an electrician's screwdriver has a plastic grip and
rubber gloves.
Non-metals such as coal (carbon), sulfur and phosphorus are dull, soft, brittle, non-
ductile, non-sonorous and poor conductors of heat and electricity.
Metal oxides are basic — burning magnesium gives magnesium oxide, whose solution
turns red litmus blue. Non-metal oxides are acidic — burning sulfur gives sulfur dioxide,
whose solution (sulfurous acid) turns blue litmus red.
Iron rusts only when both air and water are present; the slow eating away of any metal
surface by air, water or other substances is called corrosion. Rusting is prevented by
painting, oiling, greasing and galvanisation (a zinc coating).
Metals and non-metals are both elements — substances that cannot be broken into
simpler substances. 118 elements are known. Plastic, glass, wood, rubber and paper are
not elements, so they are neither metals nor non-metals.

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Class 7 Science Chapter 4 The World of Metals and Non-metals AglaSem · NCERT Solutions

Quick revision

TERM WHAT IT MEANS WHERE IT COMES EVERYDAY EXAMPLE
IN THE CHAPTER

Metallic lustre The shine shown by the surface of Section 4.1.1, page A freshly cut piece of
a metal 43 aluminium, a polished steel
plate

Malleability The property by which a material Section 4.1.1, page Silver foil (vark) on sweets,
can be beaten into thin sheets 43 aluminium foil for wrapping
rotis

Brittle Breaks into pieces on hammering Page 44 A lump of coal, a piece of
instead of flattening sulfur, a clay kulhad

Ductility The property by which a material Section 4.1.2, page Copper wire in a fan, the
can be drawn into wires 44 strings of a sitar or veena

Sonority The property of metals of Section 4.1.3, page The school bell, ghungroos,
producing a ringing sound 46 a steel plate falling down

Conduction Transfer of heat from one point of a Section 4.1.4, page A steel spoon left in hot tea
material to another 47 becomes hot at the top

Good conductor of A material that lets electricity pass Section 4.1.5, page Copper wiring in the house,
electricity through it easily 48 an iron nail in a tester

Poor conductor of A material that does not let Section 4.1.5, page Rubber gloves, the plastic
electricity electricity pass through it 48 handle of a screwdriver

Rust The brown deposit formed on iron Section 4.2, page 50 Brown flakes on an old gate
in the presence of both air and left in the rain
water

Corrosion Gradual deterioration of a metal Page 50 Green coating on a copper
surface by air, water or other vessel, black coating on
substances silver

Galvanisation Coating iron with a protective layer Page 50 Galvanised iron buckets and
of zinc metal roofing sheets

Element A substance that cannot be broken Page 53 Oxygen, carbon, iron, gold
down into simpler substances; 118 — but not plastic or glass
are known

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