Class 7 Science: The World of Metals and Non-metals MCQs (NCERT)
110 practice questions on The World of Metals and Non-metals, a chapter in the NCERT Class 7 Science textbook, with a dedicated set on Physical Properties of Metals and Non-Metals. Every question includes a written explanation. Pick a topic below, or try the samples first.
An iron sheet is weighed, left outdoors until it is well rusted, then dried completely and weighed again. It is found to be heavier than before. What is the reason?
AThe iron underneath has become more tightly packed during the rusting
BThe rust is still holding water inside its cracks, which adds to the weight
CMaterial from the air and the water has joined with the iron to form rust
DNothing has been added, so the balance must be faulty
Show answer and explanation
Correct answer: C - Material from the air and the water has joined with the iron to form rust
Rust is formed when iron combines with substances from the air and the moisture around it, so the rusted sheet contains more material than the plain iron did. The sheet was dried completely, so trapped water cannot explain the gain. Packing the same iron more tightly would not change its weight. The gain is real and expected, so the balance is not at fault.
Q2
easy
Rust is best described as
Airon that has been painted brown to protect it
Ba layer of dust that has settled on iron and stuck to its surface
Cthe same iron, only wet
Da new substance formed from iron, with properties of its own
Show answer and explanation
Correct answer: D - a new substance formed from iron, with properties of its own
Rust is not iron in a new shape; it is a different substance formed when iron meets air and moisture, and it looks and behaves quite unlike iron. Wet iron dries and shines again, while rust stays. Nobody paints a gate with rust; it appears on its own. Dust can be wiped off, but rust cannot.
Q3
medium
An iron gate that shone when it was new now looks dull and brown. What has happened to it?
AThe gate has lost its lustre because someone has painted it
BAir and moisture have formed a layer on the surface that hides the shine
CIron loses its shine as soon as it is cut to size
DThe iron all the way through the gate has slowly turned into a dull non-metal
Show answer and explanation
Correct answer: B - Air and moisture have formed a layer on the surface that hides the shine
Iron left in damp air becomes coated with a rough brown layer of rust, and that layer covers the shining metal underneath. The iron below is still iron and still a metal, not a non-metal. Nothing suggests anyone painted the gate, and a dull brown coating that forms by itself is rust. Freshly cut iron does shine, so cutting is not what dulls it.
Q4
hard
Aluminium is used for the long overhead cables that carry electricity between towns. Which combination of properties makes it suitable for this job?
AIt conducts electricity, can be drawn into long wires, and is light
BIt rusts quickly, so it needs no protective coating and costs less to keep up
CIt is a poor conductor but extremely hard, so it does not sag
DIt is sonorous, brittle and heavy
Show answer and explanation
Correct answer: A - It conducts electricity, can be drawn into long wires, and is light
An overhead cable must carry current, exist as a long unbroken wire, and stay light enough for towers to hold it over a wide span, and aluminium meets all three needs. A brittle material would snap while being drawn out. A poor conductor could not carry the current at all. Rusting would weaken a cable, so it could never be an advantage.
Q5
medium
Iron left in damp air takes weeks to show rust, while sodium reacts with water in seconds. What does this comparison show?
ADifferent metals react with water at very different speeds
BAll metals react with water at the same speed
CIron reacts faster than sodium, but the change is hidden
DOnly sodium can react with water, and iron never does
Show answer and explanation
Correct answer: A - Different metals react with water at very different speeds
The same test, water, gives a violent result with one metal and a slow one with another, so speed of reaction varies from metal to metal. Equal speeds would contradict what is seen. Iron clearly does react with air and moisture, since rust appears. Nothing about rusting is hidden; it is plainly visible and slow.
Q6
hard
A student wants to decide whether an unknown solid is a metal. Which set of observations would give the clearest answer?
AIt is heavy for its size and has a smooth surface
BIt shines when scraped, flattens under a hammer, and lights the bulb of a tester
CIt sinks in water and gives off no smell
DIt is grey in colour, feels cold to the touch and is too hard to scratch with a nail
Show answer and explanation
Correct answer: B - It shines when scraped, flattens under a hammer, and lights the bulb of a tester
Lustre, malleability and conduction are the properties actually used to identify metals, and three agreeing results make the answer safe. Colour, coldness and hardness are shared by many non-metals such as stone. Weight and smoothness depend on the object rather than on the group. Sinking and having no smell are true of chalk and glass as well.
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