Class 7 Science · Original EZT practice
The World of Metals and Non-metals (Class 7 Chapter 4): summary and practice
Why are bells made of metal, wires of copper, and why does a forgotten bicycle turn brown in the rain? Chapter 4 answers all three with a handful of tests you can do at home or watch in class: bend it, stretch it, tap it, heat it, then leave it out in air and water and see what happens. All questions are original EZT tutor practice following the chapter's own section order.
7 original worked examples, 7 fresh self-check questions and 4 mixed questions, with explained answers. These are not copied textbook exercises, an official chapter index or a full answer key. No affiliation with NCERT is claimed.
Official sources for topic and edition context, checked 18 October 2026:
1. The five property tests
Malleability - can it be beaten into thin sheets? Metals can; a lump of coal cannot. Ductility - can it be drawn into wires? Copper and aluminium can, which is why electric wires are metal. Sonority - does it ring when struck? Metals do (that is why bells and plates are metal); wood and coal do not. Conduction of heat - metals let heat travel through them (a metal spoon in hot tea warms your fingers; a wooden spoon does not). Conduction of electricity - metals let current pass; non-metals generally do not.
2. Air, water and iron: the rusting question
Iron left in the open develops brown deposits - rust. The chapter's investigation compares three conditions: dry air only, water only, and both air and water. Rust forms when BOTH air and water act on iron together.
3. What air does to other metals - and to non-metals
Magnesium ribbon, cleaned with sandpaper and burnt (teacher demonstration), forms a white powder - magnesium oxide. Dissolved in water, that oxide turns red litmus blue: it is basic. Generally, oxides of metals are basic in nature. Non-metals behave differently: burning sulphur (demonstrated in a fume hood or well-ventilated area) forms an oxide whose solution behaves the opposite way - non-metal oxides are generally acidic.
4. Non-metals matter too
Metals dominate daily objects, but life itself runs on non-metals - the oxygen we breathe is a non-metal. The point of the chapter's close: usefulness is not a metals-only club.
Choose, solve, check, then try a fresh question.
Before calculating, read the method prompt and name the condition that makes it useful. Write your own attempt. Open the steps only when you need them, and use the check to catch a wrong sign, unit or interpretation. Finish with the fresh question before reading its answer.
Choose the metal for a school bell
Choose the method: Test the two jobs the bell must do: ring loudly and keep its shape.
EZT practice question
A school bell must ring loudly when struck and keep its shape for years. Which two metal properties make it suitable?
Show the worked solution
- Striking must produce a ringing sound - that is sonority, a metal property.
- Keeping its shape for years needs the strength and hardness typical of metals.
Answer: Sonority (it rings) and the strength or hardness typical of metals.
Check: A wooden "bell" would fail the sonority test.
Watch for this: Do not answer with appearance; the choice rests on tested properties.
Now try it yourself
Which property lets a goldsmith flatten gold into foil?
Check your answer
Malleability.
Malleability is the ability to be beaten into thin sheets.
Explain copper in wires but not coverings
Choose the method: Match each part of the wire to the property it needs.
EZT practice question
Copper is used for electric wiring, not for the outer covering of the wire. Explain using two properties.
Show the worked solution
- Copper is ductile, so it can be drawn into long thin wires.
- Copper conducts electricity, so current passes through it.
- The covering must NOT conduct - so it is made of a non-metal material like plastic or rubber.
Answer: Copper is ductile and conducts electricity, suiting the core; the covering must not conduct, so it uses plastic or rubber.
Check: One property explains the shape (ductility) and another the function (conduction).
Watch for this: Do not give only conduction; without ductility copper could not be drawn into wire.
Now try it yourself
A metal spoon and a wooden spoon sit in the same hot soup. Which spoon warms your fingers first, and why?
Check your answer
The metal spoon - metals conduct heat.
Conduction lets heat travel through the metal to your fingers; wood does not conduct.
Predict rusting in three conditions
Choose the method: Check which nails meet both conditions - air and water - at once.
EZT practice question
Three identical iron nails are kept: (A) in a dry, closed jar, (B) fully under boiled water with no air above it, (C) half-dipped in water open to air. Predict what happens to each.
Show the worked solution
- A stays bright - dry air alone does not rust iron.
- B stays largely rust-free - water alone without air cannot do it.
- C rusts, worst near the waterline - air and water together make rust.
Answer: Only C rusts, worst at the waterline, because rust forms when air and water act on iron together.
Check: Each prediction follows the both-conditions rule.
Watch for this: Do not expect B to rust fastest; without air, water alone can barely rust iron.
Now try it yourself
Name the two things needed together for iron to rust.
Check your answer
Air (oxygen) and water.
The three-nail investigation shows neither alone is enough.
Explain why ships and gates need painting
Choose the method: Ask what the paint layer keeps apart.
EZT practice question
Why do ships and outdoor iron gates need regular painting?
Show the worked solution
- Paint seals the iron away from air and water at the same time.
- Scratch the paint off, both reach the metal, and rusting starts.
- So the coating must be renewed.
Answer: Paint blocks air and water together; when it wears off, both reach the iron and rusting starts, so the coating must be renewed.
Check: The explanation uses the same air-plus-water rule as the nail experiment.
Watch for this: Do not say paint only improves looks; it is a barrier against both rust conditions.
Now try it yourself
Why does an iron cycle frame rust faster in the rainy season than in winter?
Check your answer
Rain supplies water while air is always present - both conditions are met together.
Rusting speeds up when air and water act on the iron at the same time.
Read the litmus result for magnesium oxide
Choose the method: Burn the metal, dissolve the ash, then test with both litmus colours.
EZT practice question
A strip of magnesium is burnt and the white ash is dissolved in water. What happens to red and blue litmus papers dipped in that solution, and what does it show?
Show the worked solution
- Red litmus turns blue.
- Blue stays blue.
- The solution is basic - showing that magnesium oxide, a metal oxide, is basic in nature.
Answer: Red litmus turns blue and blue stays blue; the solution is basic, so magnesium oxide is a basic metal oxide.
Check: A basic solution turns red litmus blue and leaves blue litmus unchanged.
Watch for this: Do not report only one paper; the pair together shows the result.
Now try it yourself
What colour change shows that magnesium oxide solution is basic?
Check your answer
Red litmus turns blue.
A basic solution changes red litmus to blue.
Judge: do all oxides behave alike?
Choose the method: Compare a metal oxide with a non-metal oxide on indicators.
EZT practice question
"All oxides behave alike in water." True or false?
Show the worked solution
- Metal oxides are generally basic - magnesium oxide turns red litmus blue.
- Non-metal oxides like sulphur's oxide are generally acidic.
- The two have opposite effects on indicators.
Answer: False - metal oxides are generally basic while non-metal oxides are generally acidic.
Check: One example of each kind is enough to break the claim.
Watch for this: Do not generalise from one metal oxide to every oxide.
Now try it yourself
Why is the magnesium experiment done by the teacher and the sulphur one in a fume hood?
Check your answer
Burning magnesium is dazzling and hot; burning sulphur produces harmful gases.
Both are safety demonstrations, not student experiments.
Show that non-metals matter too
Choose the method: Look beyond objects to the air we breathe.
EZT practice question
Give one life-essential non-metal and one everyday reason it matters.
Show the worked solution
- Oxygen is a non-metal.
- We cannot survive without breathing it.
Answer: Oxygen - we cannot survive without breathing it.
Check: The example shows usefulness is not a metals-only club.
Watch for this: Do not answer with a metal; the question asks for a non-metal.
Now try it yourself
Name one non-metal you met in this chapter and its use or effect.
Check your answer
Sulphur - its oxide shows acidic behaviour.
Oxygen for breathing is another correct example.
Try a mixed set
Choose a method or explanation before opening each answer.
1. What is malleability?
Show answer and reason
The ability of a material to be beaten into thin sheets.
Metals have it; a lump of coal does not.
2. Why are electric wires made of metal?
Show answer and reason
Metals are ductile and conduct electricity.
Copper and aluminium can be drawn into wires and let current pass.
3. What does the three-nail investigation prove?
Show answer and reason
Rusting needs air and water together.
Nails in dry air alone or in air-free water alone stay largely bright.
4. Are metal oxides acidic or basic?
Show answer and reason
Generally basic.
Magnesium oxide solution turns red litmus blue.
Try it yourself
Work these on paper before checking any notes. Answers are deliberately not shown here.
- Why are bells and plates made of metal rather than wood?
- A scratched bicycle is left out through the monsoon. Explain what happens at the scratch.
- Why can the sulphur-burning demonstration not be done at your desk?
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Questions about this practice page
- What is the difference between malleability and ductility?
- Malleability is beating into thin sheets; ductility is drawing into wires. Both are typical metal properties, but they describe different shaping.
- Does iron rust in water alone?
- No - the chapter's investigation shows rusting needs air AND water together. Dry air alone or air-free water alone leaves iron largely unrusted.
- Are metal oxides acidic or basic?
- Generally basic - burnt magnesium's white oxide turns red litmus blue in solution.
- Which metals conduct electricity best for household wiring?
- The chapter's point is that metals conduct; copper (and aluminium) are the practical wiring metals because they are ductile and good conductors.
- Are these the NCERT exercise questions for The World of Metals and Non-metals?
- No. EZT pages are original practice written by our tutors, aligned to the chapter's syllabus - use them to prepare for the textbook exercises, not as a substitute for your book.