Solutions-NCERT-Class-7-Science-Curiosity-Chapter-4-The World of Metals and Non-metals-CBSE

Objects that are lustrous (shiny) in appearance and hard are usually metals.
Examples include:

• Gold jewellery
• Silver coins
• Iron tools (like hammer, nails)
• Steel utensils
• Copper vessels

These objects are shiny and strong because they are made of metals.

No, not all metals are hard and solid. Sodium and potassium are soft and can be cut with a knife, whereas mercury is a liquid metal at room temperature.

Objects made of metals become flat when beaten with a hammer.
Examples are:

• Aluminium sheet or foil
• Copper sheet
• Iron sheet
• Gold or silver sheet

This happens because metals are malleable, which means they can be beaten into thin sheets.

Examples of metal sheets are

• Thin silver foil used on sweets and
• Aluminium foil used for wrapping food.
• Steel sheets – used in cars, appliances, and containers
• Copper sheets – used in electrical work and decorations

Metal wires are used in electrical fittings, ornaments like bangles and necklaces, and musical instruments like veena, sitar, violin, and guitar.

No, coal and sulphur are not ductile, so wires cannot be made from them.

• When a metal spoon or plate is dropped, it produces a clear, ringing sound.
  But when coal or wood is dropped, it produces a dull or soft sound.
• This is because metals are sonorous (they produce a ringing sound), while coal and wood are non-sonorous.

Metals like copper and aluminium are used for making cooking vessels because they are good conductors of heat.

The handle of a screwdriver is made of plastic which is a poor conductor of electricity.

An electrician wears rubber gloves and shoes because rubber is a poor conductor of electricity and protects against electric shock.

Materials like iron and copper, which are metals, make the bulb glow.

Materials that allow electricity to pass through them easily are called good conductors of electricity.

An iron object develops brown deposits when it comes into contact with both air and water.

Rusting of iron can be prevented by painting, oiling, greasing, or coating it with zinc (galvanisation).

When magnesium ribbon burns, it forms a basic oxide that turns red litmus paper blue.

• Sodium is stored in kerosene because it is very reactive.
• It reacts quickly with air and moisture and may catch fire.
• Kerosene keeps sodium away from air and water, so it prevents fire and accidents.

When sulphur burns in air, it forms sulphur dioxide gas, which dissolves in water to form sulphurous acid.

No, sulphur does not react with water like metals do.

Non-metals are usually soft, dull, not malleable or ductile, not sonorous, and are poor conductors of heat and electricity. Their oxides are generally acidic.

Examples of non-metals are oxygen, hydrogen, nitrogen, carbon, etc.

No, plastic, glass, wood, and rubber are not classified as metals or non-metals because they are not elements.

Non-metals are important in our lives because they play a vital role in living, farming, and daily needs.

• Oxygen is needed for breathing.
• Carbon is the basic element of all living things.
• Nitrogen helps plants grow and is used in fertilisers.
• Chlorine is used to purify drinking water.
• Iodine is used as an antiseptic to clean wounds.

Thus, non-metals are essential for life, health, agriculture, and sanitation.

(i) Aluminium

(iv) Sodium

(i) False. Aluminium and copper are metals and not non-metals which are used for making utensils and statues.

(ii) False. Metallic oxides are basic in nature and the solution of which turns red litmus paper to blue.

(iii) True

(iv) False. Copper vessels are used for boiling water because copper is a good conductor of heat, not electricity.

Only a few metals are suitable for making jewellery because they have special properties.

• They are lustrous, so they look shiny and attractive.
• They are malleable, so they can be easily shaped into different designs.
• They do not rust or corrode easily, so they last for a long time.

Metals like gold, silver, and platinum have these properties, which is why they are used for jewellery.

(i)-(c), (ii)-(e), (iii)-(a), (iv)-(d), (v)-(b)

(i) Used in electrical wiring - (c) Copper

(ii) Most malleable and ductile - (e) Gold

(iii) Living organisms cannot survive without it-(a) Oxygen

(iv) Plants grow healthy when fertilisers containing it are added to the soil - (d) Nitrogen

(v) Used in water purification - (b) Chlorine

When oxygen reacts with magnesium and sulfur, different types of products are formed.

• Magnesium burns in oxygen with a bright white flame and forms magnesium oxide, which is a basic oxide.
• Sulfur burns in oxygen with a blue flame and forms sulfur dioxide, which is an acidic oxide.

Main differences in the products formed:

• Magnesium oxide is basic in nature and reacts with acids.
• Sulfur dioxide is acidic in nature and reacts with bases.

So, oxygen forms a basic oxide with a metal (magnesium) and an acidic oxide with a non-metal (sulfur).

I would choose copper to make a pan for boiling water because it is a good conductor of heat and heats water quickly and evenly.

The iron nail dipped in oil will not rust because oil prevents air and water from reaching the surface of the iron and stops rusting.

The different properties of metals and non-metals decide how we use them in daily life.

Metals are generally hard, strong, malleable, ductile, shiny, and good conductors of heat and electricity.

Because of these properties:

• Iron and steel are used to make buildings, bridges, and tools.
• Copper and aluminium are used for electrical wires.
• Aluminium is used in aeroplanes because it is light and does not rust.
• Gold and silver are used for jewellery because they are shiny and easy to shape.

Non-metals are usually light, dull, poor conductors of heat and electricity, and many are essential for life.

Because of these properties:

• Oxygen is used for breathing.
• Nitrogen is used in fertilisers for plant growth.
• Chlorine is used to purify water.
• Carbon is used as fuel and is the basis of all living things.

Thus, the special properties of metals and non-metals decide their different uses in everyday life.

No, sulfur cannot be used to protect iron from rusting.

• Rusting happens when iron reacts with oxygen and moisture. Zinc protects iron because it forms a protective layer and also reacts with oxygen more easily than iron, preventing iron from rusting (this process is called galvanisation).
• Although sulfur does not react with water, it does not form a protective coating on iron. In fact, sulfur can react with iron to form iron sulfide, which damages the iron instead of protecting it.

Therefore, sulfur cannot be used to protect iron from rusting, while zinc is suitable for this purpose.

• Heating is necessary because iron becomes soft and more malleable when heated. This makes it easier to shape, bend, and beat into tools.
• If iron is not heated, it is very hard and difficult to mould.