NCERT Solutions Class 7 Science Curiosity Chapter 04 The World of Metals and Non-Metals

Class 7 Science Curiosity Chapter 4 Solutions

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Question 1. 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
Answer: (i) Aluminium
Aluminium foil is widely used to wrap food items. This is because metals can be beaten into very thin sheets without breaking. This special property is called malleability.
In simple words: Aluminium is used to wrap food. It is cheap and can be flattened into thin sheets easily.

Exam Tip: Remember that the ability of metals to be beaten into thin sheets is called malleability, and aluminium is a perfect example of this.

Question 2. Which of the following metal catches fire when it comes in contact with water?
(i) Copper
(ii) Aluminium
(iii) Zinc
(iv) Sodium
Answer: (iv) Sodium
Sodium reacts very quickly and strongly with water and air. This reaction produces a lot of heat and can start a fire. To keep it safe, sodium is stored under kerosene oil.
In simple words: Sodium is very reactive. It catches fire when it touches water or air, so it is kept in kerosene.

Exam Tip: Sodium is highly reactive, which is why it must be stored in kerosene to keep it away from moisture and air.

Question 3. 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. [ ]
Answer:
(i) **[F] False.** Aluminium and copper are metals, not non-metals. They are shiny, hard, and strong.
(ii) **[F] False.** When metals combine with oxygen, they make basic oxides. These basic mixtures turn red litmus paper to blue, not blue to red.
(iii) **[T] True.** Oxygen is a non-metal. We and other living things need it to breathe and stay alive.
(iv) **[F] False.** Copper pots are used for boiling water because copper is a great conductor of heat. This lets the heat pass into the water quickly. It is not because of electricity.
In simple words: Aluminium and copper are metals. Metal oxides are basic and turn red litmus blue. Oxygen is a non-metal we breathe. Copper boils water because it conducts heat well.

Exam Tip: Pay attention to the terms "metal" and "non-metal" and "heat" versus "electricity" to avoid simple traps in True or False questions.

Question 4. Why are only a few metals suitable for making jewellery?
Answer: Only some metals are used for jewellery because they need special properties. First, they must have lustre, which means they are shiny. Second, they need to be malleable and ductile so they can be shaped into beautiful designs and drawn into thin wires. Third, they must not rust or tarnish easily. Lastly, they are rare and valuable. Gold and silver are perfect examples because they have all these features.
In simple words: We use gold and silver for jewellery because they are shiny, easy to shape, do not rust easily, and are rare.

Exam Tip: When explaining jewellery metals, highlight four key terms - lustre (shine), malleability (shaping), ductility (wires), and resistance to corrosion.

Question 5. 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.

Answer: The correct matches with the unjumbled names are:
(i) Used in electrical wiring - (c) COPPER (unjumbled from PEPORC)
(ii) Most malleable and ductile - (e) GOLD (unjumbled from OGDL)
(iii) Living organisms cannot survive without it - (a) OXYGEN (unjumbled from ENXYGO)
(iv) Plants grow healthy when fertilisers containing it are added to the soil - (d) NITROGEN (unjumbled from TENGOINR)
(v) Used in water purification - (b) CHLORINE (unjumbled from NECOHIRL)
In simple words: Unjumble the letters to find the correct metal or non-metal. Copper is for wires, gold is easy to shape, oxygen is for breathing, nitrogen is for plants, and chlorine cleans water.

Exam Tip: Match the functions carefully and practice unjumbling the element names to ensure you don't make spelling errors.

Question 6. What happens when oxygen reacts with magnesium and sulfur. What are the main differences in the nature of products formed?
Answer: When magnesium (which is a metal) burns in oxygen, it creates magnesium oxide. When sulfur (which is a non-metal) burns in oxygen, it creates sulfur dioxide gas. The main difference is that magnesium oxide forms a basic solution when dissolved in water. On the other hand, sulfur dioxide forms an acidic solution in water. As a general rule, metal oxides are basic, while non-metal oxides are acidic.
In simple words: Burning magnesium makes magnesium oxide, which is basic. Burning sulfur makes sulfur dioxide, which is acidic.

Exam Tip: Remember the general rule - metal oxides are basic (turn red litmus blue) and non-metal oxides are acidic (turn blue litmus red).

Question 7. Complete the following flow chart: (Flow chart depicts burning magnesium)
Answer: Here is the completed flow chart:
The missing parts from the flow chart are:
1. **Starting Material (?):** Magnesium ribbon
2. **Ash:** Magnesium oxide
3. **Solution (?):** Magnesium hydroxide solution
4. **Change in blue litmus:** No change
5. **Conclusion (?):** The solution is basic In simple words: When you burn magnesium ribbon in air, it turns to ash (magnesium oxide). Mixing this ash with water makes a basic solution that turns red litmus paper blue.

Exam Tip: In flowcharts, make sure to write down both the chemical name (like Magnesium hydroxide) and its properties (like being basic) to show complete understanding.

Question 8. 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
Answer: The most suitable choice would be copper or iron to make the boiling pan. This is because boiling water requires a material that can transfer heat quickly. Both copper and iron are excellent conductors of heat. On the other hand, materials such as sulfur, coal, plastic, wood, and cardboard do not conduct heat well. This makes them completely unfit for making cooking pots.
In simple words: Copper and iron are great for making pans because they let heat pass through easily. Wood, plastic, and cardboard are poor heat conductors.

Exam Tip: Always mention the property of "good conductor of heat" when explaining why metals are chosen for cooking utensils.

Question 9. You are provided with three iron nails, each dipped in oil, water and vinegar. Which iron nail will not rust, and why?
Answer: The iron nail that is kept in oil will not rust. For rusting to happen, iron needs to be in contact with both oxygen from the air and water. The layer of oil forms a protective barrier. This prevents air and moisture from touching the surface of the nail, which stops the rusting process.
In simple words: The nail in oil will not rust. This is because the oil keeps water and air from touching the nail.

Exam Tip: Remember that rusting cannot happen without both air (oxygen) and moisture (water) being present together.

Question 10. How do the different properties of metals and non-metals determine their uses in everyday life?
Answer: The way we use metals and non-metals in our daily lives depends directly on their specific characteristics:

**Metals:**
* **Conducting Electricity:** Used to make wires because they let current pass through easily.
* **Conducting Heat:** Used for making pots and pans because they transfer heat well.
* **Malleability and Ductility:** Allows them to be beaten into thin sheets or drawn into wires for making things like jewellery.
* **Strength and Durability:** Used to construct heavy machines, tools, and buildings.
* **Sonority:** Used to make bells as they produce a ringing sound.
* **Shine (Lustre):** Used for decorative items.

**Non-metals:**
* **Poor Conductivity:** Used to make handles for kitchen tools and wire coatings to keep us safe from heat and electricity.
* **Gaseous State:** Oxygen is needed for breathing, while nitrogen is used in plant fertilisers.
* **Chemical Qualities:** Chlorine helps clean water, iodine works as an antiseptic for wounds, and carbon is the basis of life.
* **Brittleness:** They break easily under pressure, so they are not used for structural support.
In simple words: Metals are strong, shiny, shapeable, and conduct heat and electricity, so we use them for structures, wires, and pans. Non-metals are poor conductors and have special chemical roles like oxygen for breathing or chlorine for cleaning water.

Exam Tip: Create a comparative list of properties (like conductivity and physical state) to explain the distinct uses of metals and non-metals clearly in exams.

Question 11. 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.
Answer: No, sulfur cannot be used to protect iron from rusting. This is because sulfur is very brittle. Unlike zinc, which forms a strong, sticky layer on iron during galvanization, sulfur does not stick well to metal surfaces. A layer of sulfur would easily crack and peel off, leaving the iron exposed to air and water.
In simple words: No, sulfur breaks too easily and will crack or fall off the iron, so it cannot stop rusting.

Exam Tip: Galvanization works because zinc forms a tough, sticking protective layer - brittle materials like sulfur cannot do this.

Question 12. An ironsmith heats iron before making tools. Why is heating necessary in this process?
Answer: Heating the iron makes it much softer and increases its malleability. When the iron is hot, the ironsmith can easily beat it with a hammer to mould and shape it into different tools without it cracking or breaking.
In simple words: Heating makes iron soft. This makes it easy for the blacksmith to hammer and shape it into tools.

Exam Tip: Focus on the term "malleability" - heating increases this property in iron, making shaping possible.

Class 7 Science Curiosity Chapter 3 Very Short Answer Type Questions

Question. What is malleability?
Answer: Malleability is the special property of a substance that lets it be hammered or flattened into very thin sheets without cracking. Most metals, including gold and aluminium, show this property.
In simple words: Malleability is when a metal can be beaten into thin sheets without breaking.

Exam Tip: Always use the key phrase "without breaking" when defining malleability to get full marks.

Question. Name two metals used to make kitchen utensils.
Answer: Two metals commonly used for cooking pots and pans are aluminium and copper. They are chosen because they conduct heat very well and are easy to shape into utensils.
In simple words: Aluminium and copper are used to make cooking pots because they carry heat well.

Exam Tip: Copper and aluminium are the most common examples of metals with high thermal conductivity.

Question. What kind of sound do metals make when struck?
Answer: When you hit a metal, it makes a clear, ringing sound. This unique property is called sonority, and metals that do this are called sonorous.
In simple words: Metals make a ringing sound when hit. This is called being sonorous.

Exam Tip: Remember the term "sonorous" - it is the scientific word for the ringing sound produced by metals.

Question. Which metal remains in liquid form at room temperature?
Answer: Mercury is the only metal that is a liquid at normal room temperature.
In simple words: Mercury is the only metal that is a liquid at room temperature.

Exam Tip: Mercury is an important exception to the rule that all metals are solid, making it a favorite exam question.

Question. What is rusting?
Answer: Rusting is when a reddish-brown layer forms on the surface of iron. This happens when iron reacts with wet air (oxygen and water). It is a form of corrosion.
In simple words: Rusting is when iron gets a brown layer on it because of wet air.

Exam Tip: Remember that rusting is a specific name for the corrosion of iron in the presence of oxygen and water.

Class 7 Science Curiosity Chapter 3 Short Answer Type Questions

Question. Why are electrical wires usually made of copper or Aluminium?
Answer: Copper and aluminium are highly efficient at carrying electric current. They are also very ductile, which means they can be stretched into long, thin wires without snapping. These features make them perfect for making household electrical wires.
In simple words: Copper and aluminium conduct electricity well and can be easily stretched into thin wires.

Exam Tip: Mention "good conductivity of electricity" and "ductility" as the two main reasons for their use in wiring.

Question. What happens when magnesium ribbon burns in air?
Answer: When a strip of magnesium is burned in air, it produces a very bright, blinding white flame and leaves behind a white powder called magnesium oxide. If you mix this powder with water, the solution turns red litmus paper blue, which proves it is basic.
In simple words: Magnesium burns with a bright white light and leaves a white powder. This powder forms a basic solution in water.

Exam Tip: Write down the observation (dazzling white flame) and the chemical nature of the product (basic oxide) in your answer.

Question. Why are metals used for making cooking utensils?
Answer: Metals such as copper and aluminium are chosen because they spread heat quickly and evenly. They are also hard and strong, which means they last a long time in the kitchen without getting damaged.
In simple words: Metals are used because they heat up fast, spread heat evenly, and are strong enough to last.

Exam Tip: Highlight both thermal conductivity (even heat distribution) and physical durability (strength) when discussing cookware.

Question. What is ductility? Give two examples of ductile metals.
Answer: Ductility is the physical property that allows a material to be stretched out into long, thin wires. Gold and copper are excellent examples of ductile metals, which is why they are used to make jewelry and electrical cables.
In simple words: Ductility means a metal can be pulled into thin wires. Gold and copper are two examples.

Exam Tip: Be clear that ductility refers to drawing into wires, whereas malleability refers to beating into sheets.

Question. Why do we store sodium metal in kerosene?
Answer: Sodium reacts very aggressively with both air and moisture. This fast reaction generates intense heat and highly flammable gases. Keeping sodium under kerosene blocks it from touching air and water, preventing any hazardous reactions.
In simple words: Sodium reacts fast with air and water, causing a fire. Storing it in kerosene keeps it safe.

Exam Tip: State clearly that sodium reacts with *both* moisture and air, and kerosene acts as a barrier to isolate the metal.

Class 7 Science Curiosity Chapter 4 Descriptive Questions

Question. Explain the difference between metals and non-metals with examples.
Answer: Metals and non-metals differ in many physical and chemical properties:

* **Metals** have a bright shine (lustre), can be beaten into sheets (malleability), and drawn into wires (ductility). They are excellent at conducting heat and electricity. Examples include iron and aluminium. They form basic oxides when burned.
* **Non-metals** are dull, break easily when hit (brittle), and do not conduct heat or electricity well. Examples include sulfur and carbon. They form acidic oxides when burned.

These differences make metals highly useful for building and wiring, while non-metals are essential for health, medicine, and farming.
In simple words: Metals are shiny, easy to shape, and conduct heat and electricity, like iron. Non-metals are dull, brittle, and poor conductors, like sulfur.

Exam Tip: Make a clear distinction between the physical states, conductivity, and chemical nature of oxides for both groups.

Question. Why does an iron nail rust when exposed to both air and water?
Answer: Rusting is a chemical reaction that takes place when iron is in contact with oxygen and water at the same time. If only one of these is present, like in dry air or boiled water without air, the nail does not rust. Moist air contains both, which triggers the formation of the reddish-brown rust on the nail.
In simple words: Iron nails rust because they react with oxygen and water together. Moist air has both, so it makes the nail rust.

Exam Tip: Emphasize that *both* oxygen and water must act on the iron simultaneously for rust to appear.

Question. Why are most handles of kitchen tools made from wood or plastic?
Answer: Wood and plastic do not transfer heat well. By using them to make handles, they stay cool and protect our hands from getting burned while we cook. If the handles were made of metals, they would heat up very quickly and become dangerous to hold.
In simple words: Wood and plastic do not get hot easily. They are used on handles to protect our hands from burns.

Exam Tip: Describe wood and plastic as "insulators of heat" or "poor conductors of heat" to secure full marks.

Question. How does the oxide of sulfur differ from the oxide of magnesium in nature?
Answer: The oxide of sulfur is acidic. Because of this, it turns damp blue litmus paper to red. Conversely, the oxide of magnesium is basic, which means it turns damp red litmus paper to blue. This shows the general rule that non-metal oxides are acidic while metal oxides are basic.
In simple words: Sulfur oxide is acidic and turns blue litmus red. Magnesium oxide is basic and turns red litmus blue.

Exam Tip: Write down the litmus test color changes explicitly to support your explanation of acidic and basic natures.

Question. What does the Iron Pillar of Delhi teach us about ancient Indian metallurgy?
Answer: The famous Iron Pillar in Delhi is more than 1600 years old and has stood in the open air without rusting. This tells us that metalworkers in ancient India had highly advanced skills. They knew how to make iron that resists corrosion using techniques that scientists are still studying today.
In simple words: The Iron Pillar has not rusted for over 1600 years. It shows that ancient Indians were very good at making high-quality metals.

Exam Tip: Use the key phrase "rust resistance" or "corrosion resistance" to describe the pillar's outstanding quality.

Class 7 Science Curiosity Chapter 4 Exploring Questions

Question. How do metals and non-metals affect our daily lives in different ways?
Answer: Metals and non-metals are both highly important in our lives in very different ways:

* **Metals** are used to build houses, roads, vehicles, and electronics. This is because they are strong, long-lasting, and conduct electricity well.
* **Non-metals** are needed for survival and growth. For instance, oxygen is essential for breathing, carbon is in all our food, nitrogen helps plants grow as a fertiliser, and iodine is applied to heal cuts.

Together, they support our health, farming, and modern technology.
In simple words: Metals are used to make strong things like cars and wires. Non-metals are essential for living, like breathing oxygen or growing plants with nitrogen.

Exam Tip: List specific everyday examples (like oxygen for breathing, metals for buildings) to write a well-rounded answer.

Question. If sulfur is soft, non-sonorous, and poor conductor, can it be used for making wires? Why or why not?
Answer: No, sulfur is not suitable for making wires. Since it lacks ductility, it will break apart easily if you try to stretch it. Also, it is a poor conductor of electricity, meaning current cannot flow through it. Metals like copper and aluminium are ductile and conduct electricity, which is why we use them instead.
In simple words: No, sulfur breaks too easily and does not carry electricity, so we cannot make wires from it.

Exam Tip: Highlight two main failures of sulfur for wiring - lack of ductility (brittleness) and low electrical conductivity.

Question. Why is the discovery of iron considered more significant in history than copper, despite copper being discovered earlier?
Answer: Even though copper was found first because it was simpler to extract, iron had a much bigger impact on human history. Iron is much stronger and harder than copper. This allowed ancient people to build far better tools for farming, stronger weapons, and sturdier buildings, helping civilizations grow quickly.
In simple words: Iron is much stronger than copper. It allowed humans to make better farming tools and stronger buildings, which helped societies grow.

Exam Tip: Contrast the structural strength of iron with copper to explain its greater historic and developmental significance.

Question. Can sulfur be used to prevent rusting of iron like zinc is used in galvanisation? Why or why not?
Answer: No, sulfur cannot be used to stop iron from rusting. Sulfur is a non-metal and is too brittle to form a solid, sticking shield over iron. On the other hand, zinc is a metal that can coat iron smoothly. This coats the iron completely, keeping water and air away.
In simple words: No, sulfur is brittle and cannot coat the iron like zinc does to protect it from air and water.

Exam Tip: Recall that galvanization specifically requires a cohesive, protective metallic layer (like zinc) that does not crack or chip.

Question. Which materials would you choose to make a pan for boiling water and why?
Answer: I would pick copper or aluminium to make a boiling pan. Both of these metals allow heat to travel through them very quickly and can tolerate high flames without melting. They are also easy to shape into pots and are strong enough to last a long time in the kitchen.
In simple words: Copper or aluminium are great because they heat up fast, don't melt easily, and can be shaped into pans.

Exam Tip: Mention heat conductivity and the high melting points of these metals to justify why they are safe for cooking.

Let’s Discuss Class 7 Science Curiosity Chapter 4

Question. Why do iron objects rust when kept in open air and water, as explained in Class 7 Science Curiosity Chapter 4?
Answer: Iron objects rust in the open because they react with oxygen and water present in the surrounding air. This chemical reaction creates a reddish-brown substance called rust. Rusting is a form of corrosion that slowly damages metal tools and buildings. If iron is kept in completely dry air, or placed in water with no air, it will not rust. But moist air has both oxygen and moisture, which causes rust to form. We can protect iron by using paint, oil, or zinc coatings.
In simple words: Iron reacts with both water and oxygen in the air to make a brown layer called rust. Paint or oil can stop this.

Exam Tip: Be ready to name three rust-prevention methods - painting, oiling, and galvanization (coating with zinc).

Question. What is the difference between the oxides formed by metals and non-metals in Class 7 Science Curiosity Chapter 4?
Answer: The main difference lies in their chemical nature:

* **Metal Oxides:** When metals like magnesium burn, they create basic oxides. If you mix them with water, they turn red litmus paper blue.
* **Non-Metal Oxides:** When non-metals like sulfur burn, they create acidic oxides. For example, sulfur dioxide forms sulfurous acid in water, which turns blue litmus paper red.

This test is a main way to tell metals and non-metals apart in a science lab.
In simple words: Metal oxides are basic and turn red litmus blue. Non-metal oxides are acidic and turn blue litmus red.

Exam Tip: Remember that litmus paper tests are the easiest way to identify whether an oxide is metallic (basic) or non-metallic (acidic).

Question. Why can metals be used for making wires but non-metals cannot, as mentioned in Class 7 Science Curiosity Chapter 4?
Answer: Metals can be turned into wires because they are ductile. This means they can be stretched into long, thin strands without snapping. Copper and aluminium are excellent examples. They are also very good at conducting electricity. Non-metals, like sulfur or coal, are brittle and crumble when you try to pull them. They also do not conduct electricity, so they cannot be used for wires.
In simple words: Metals are ductile and carry electricity well, so they make good wires. Non-metals break easily and do not carry electricity.

Exam Tip: Wires need two physical features - ductility (to be shaped into wires) and electrical conductivity (to carry current).

Question. Is it necessary to do all the experiments in Class 7 Science Curiosity Chapter 4?
Answer: While you might not need to perform every experiment in a lab, understanding them is highly important. Doing or watching these activities helps you see how metals and non-metals react in real life. It makes concepts like rusting, burning of magnesium, and testing with litmus paper much easier to understand and remember for your exams.
In simple words: Doing the experiments helps you understand science better. It makes it easier to remember how metals behave.

Exam Tip: Pay close attention to the observations and conclusions of each experiment, as these are often asked directly in exams.

Question. What is the easiest way to remember the difference between metals and non-metals in Class 7 Science Curiosity Chapter 4?
Answer: The easiest way to remember the differences is to make a simple comparative table. Group their properties into physical traits (like shine, hardness, and shape) and chemical traits (like how they react with water or oxygen). You can also think of common daily items, like a copper wire (metal) and charcoal (non-metal), to help you visualize these differences.
In simple words: Make a table comparing their traits. Think of a copper wire and coal to remember how they differ.

Exam Tip: Practicing a comparison table is highly recommended, as it is a common five-mark question in science exams.

Question. Do I need to remember all the properties of metals and non-metals for Class 7 Science Curiosity Chapter 4?
Answer: Yes, it is very helpful to remember the main properties. You should focus on key terms like malleability, ductility, sonority, and heat or electrical conductivity. Knowing these properties will help you explain why different materials are used to make everyday objects like wires, pots, and tools.
In simple words: Yes, you should learn the main properties like shine, conductivity, and strength because they explain how we use metals and non-metals.

Exam Tip: Focus on the key terms and definitions of physical properties, as they form the foundation of almost all questions in this chapter.