CBSE Class 10 Science (2026–27)
Chapter 3: Metals and Non-Metals
20 Important Questions with Answers
Metals and non-metals are classified based on their physical and chemical properties, reactions, reactivity series, ionic compounds, corrosion, and metallurgy.
1. What are metals? Mention any four physical properties of metals.
Answer:
Metals are elements that generally lose electrons to form positive ions and are good conductors of heat and electricity. They possess several characteristic physical properties. Firstly, metals are lustrous, meaning they have a shiny surface. Secondly, they are malleable, so they can be beaten into thin sheets. Thirdly, metals are ductile, allowing them to be drawn into wires. Finally, they are sonorous, producing a ringing sound when struck. Most metals are also hard and have high melting and boiling points. These properties make metals useful in manufacturing utensils, machinery, electrical wires, and construction materials. Examples include iron, copper, aluminium, and silver.
2. What are non-metals? State four important properties of non-metals.
Answer:
Non-metals are elements that generally gain electrons to form negative ions during chemical reactions. They possess properties opposite to those of metals. Non-metals are usually dull and do not have a shiny appearance. They are generally brittle, meaning they break easily when hammered. Most non-metals are poor conductors of heat and electricity. They are also non-sonorous, so they do not produce a ringing sound when struck. Many non-metals exist as gases at room temperature, such as oxygen and nitrogen. Some exceptions also exist; for example, graphite conducts electricity and iodine has a lustrous appearance. Examples of non-metals include sulphur, phosphorus, carbon, and oxygen.
3. Why is sodium stored under kerosene oil?
Answer:
Sodium is a highly reactive metal that reacts vigorously with oxygen and moisture present in the atmosphere. When exposed to air, it quickly forms sodium oxide. In the presence of water, sodium reacts violently, producing sodium hydroxide and hydrogen gas along with a large amount of heat. This heat may ignite the hydrogen gas, causing fire or explosions. To prevent such dangerous reactions, sodium is stored under kerosene oil. The kerosene layer isolates sodium from air and moisture, thereby protecting it from oxidation and accidental ignition. Potassium is also stored in a similar manner because it is even more reactive than sodium.
4. Explain the reaction of metals with oxygen.
Answer:
Metals react with oxygen to form metal oxides. Most metal oxides are basic in nature and react with acids to form salt and water. For example, magnesium burns in air with a dazzling white flame to produce magnesium oxide.
2Mg + O₂ → 2MgO
Some metal oxides, such as aluminium oxide and zinc oxide, show both acidic and basic properties and are called amphoteric oxides. Metal oxides generally protect the metal surface from further corrosion by forming a protective layer. The reaction with oxygen demonstrates the chemical reactivity of metals and helps in understanding their behavior in different environments.
5. Describe the reaction of metals with water.
Answer:
Different metals react with water at different rates depending on their reactivity. Highly reactive metals such as sodium and potassium react vigorously with cold water, producing metal hydroxides and hydrogen gas. Calcium reacts less vigorously, while magnesium reacts with hot water. Metals like iron react only with steam. Copper, silver, and gold do not react with water. For example:
2Na + 2H₂O → 2NaOH + H₂ + Heat
The reaction produces hydrogen gas, which can be identified by a popping sound when a burning splint is brought near it. This reaction helps determine the relative reactivity of metals.
6. How do metals react with dilute acids?
Answer:
Most metals react with dilute acids to form a salt and hydrogen gas. The reaction occurs because metals displace hydrogen from acids due to their greater reactivity. For example:
Zn + H₂SO₄ → ZnSO₄ + H₂
The evolved hydrogen gas can be tested by bringing a burning splint near it, which produces a characteristic popping sound. However, metals such as copper, silver, gold, and platinum do not react with dilute hydrochloric acid or dilute sulphuric acid because they are less reactive than hydrogen. This reaction is important in understanding the reactivity series of metals and their chemical behavior.
7. What is the reactivity series? Why is it important?
Answer:
The reactivity series is a list of metals arranged in decreasing order of their reactivity. The series is:
K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Ag > Au
This series helps predict how metals will react with water, acids, and salt solutions. A metal higher in the series can displace a metal lower in the series from its compound. The reactivity series is also useful in metallurgy for determining suitable methods of extraction. It helps scientists understand corrosion, displacement reactions, and industrial processes involving metals. Thus, the reactivity series is an essential tool in chemistry.
8. What is a displacement reaction? Give an example.
Answer:
A displacement reaction is a chemical reaction in which a more reactive metal displaces a less reactive metal from its salt solution. The reaction occurs because the more reactive metal has a greater tendency to lose electrons and form positive ions. For example:
Zn + CuSO₄ → ZnSO₄ + Cu
In this reaction, zinc displaces copper from copper sulphate solution because zinc is more reactive than copper. The blue colour of copper sulphate gradually fades, and reddish-brown copper is deposited. Displacement reactions help compare the reactivity of metals and are widely used in industrial and laboratory processes.
9. What are ionic compounds?
Answer:
Ionic compounds are compounds formed by the transfer of electrons from one atom to another. Metals lose electrons to form positive ions, while non-metals gain electrons to form negative ions. The oppositely charged ions attract each other through strong electrostatic forces, resulting in the formation of ionic compounds. For example, sodium chloride (NaCl) is formed when sodium transfers one electron to chlorine. Ionic compounds are generally hard, crystalline solids with high melting and boiling points. They conduct electricity in molten or aqueous states but not in the solid state because ions become free to move only when dissolved or melted.
10. State any four properties of ionic compounds.
Answer:
Ionic compounds possess several unique properties due to strong electrostatic forces between ions.
- They are generally hard and solid at room temperature.
- They have high melting and boiling points.
- They are soluble in water but insoluble in organic solvents.
- They conduct electricity in molten and aqueous states but not in solid form.
These properties arise because ions are held together by strong forces of attraction. Breaking these forces requires a large amount of energy, resulting in high melting points. Examples include sodium chloride, magnesium oxide, and calcium chloride. These compounds are widely used in daily life and industrial applications.
11. Why do ionic compounds conduct electricity in molten state but not in solid state?
Answer:
In the solid state, ions in an ionic compound are tightly packed and fixed in position by strong electrostatic forces. Since the ions cannot move freely, they cannot carry electric current. However, when the compound is melted or dissolved in water, these ions become free to move. The movement of positive and negative ions allows the conduction of electricity. Therefore, ionic compounds conduct electricity in molten and aqueous states but not in solid form. This property is an important characteristic used to identify ionic compounds and understand their behavior in chemical and industrial processes.
12. What is corrosion?
Answer:
Corrosion is the gradual deterioration of metals due to chemical reactions with their surroundings, such as air, moisture, or chemicals. The most common example is rusting of iron. During rusting, iron reacts with oxygen and water to form hydrated iron oxide, commonly known as rust. Corrosion weakens metals and causes economic losses by damaging machinery, vehicles, bridges, and buildings. Factors such as humidity and pollutants accelerate corrosion. The process can be controlled through painting, oiling, galvanization, alloying, and electroplating. Preventing corrosion increases the durability and efficiency of metallic objects.
13. What are alloys? Give two examples.
Answer:
Alloys are homogeneous mixtures of two or more metals, or a metal and a non-metal, prepared to improve properties such as strength, hardness, corrosion resistance, and durability. Alloys are usually stronger and more useful than pure metals. For example, brass is an alloy of copper and zinc, while bronze is an alloy of copper and tin. Stainless steel is another important alloy made of iron, chromium, and nickel. Alloys are used in making utensils, machinery, tools, coins, and construction materials. Their enhanced properties make them suitable for various industrial and domestic applications.
14. Differentiate between metals and non-metals.
Answer:
Metals and non-metals differ in many physical and chemical properties. Metals are generally lustrous, malleable, ductile, and good conductors of heat and electricity. They lose electrons and form positive ions. Non-metals are usually dull, brittle, and poor conductors of heat and electricity. They gain electrons and form negative ions. Metals produce basic oxides, whereas non-metals generally form acidic oxides. Examples of metals include iron and copper, while sulphur and oxygen are common non-metals. These differences help scientists classify elements and predict their behavior in chemical reactions.
15. Why are metals good conductors of electricity?
Answer:
Metals are good conductors of electricity because they contain free electrons that can move easily throughout the metallic structure. When an electric potential is applied, these electrons flow in a specific direction, carrying electric current. The presence of mobile electrons also explains why metals conduct heat efficiently. Copper and silver are among the best electrical conductors and are widely used in electrical wiring and electronic devices. The conductivity of metals makes them essential in power transmission, electrical appliances, and industrial machinery. This property is one of the most important characteristics of metals.
16. What is galvanization? Why is it done?
Answer:
Galvanization is the process of coating iron or steel with a thin layer of zinc to protect it from rusting. Zinc acts as a protective barrier and prevents oxygen and moisture from reaching the iron surface. Even if the zinc coating is scratched, zinc corrodes preferentially and protects the iron underneath. Galvanization is widely used in making water pipes, roofing sheets, fences, and storage tanks. This method significantly increases the lifespan of iron objects and reduces maintenance costs. Therefore, galvanization is an effective and economical technique for preventing corrosion.
17. Explain the extraction of metals low in the reactivity series.
Answer:
Metals low in the reactivity series, such as mercury and copper, are relatively easy to extract from their ores. Their sulphide ores are first heated in air to convert them into oxides. The metal oxide is then heated further, causing decomposition and yielding the metal. Since these metals are less reactive, they can often be obtained by simple reduction processes. For example, mercury is extracted from cinnabar ore (HgS). The extraction process requires less energy compared to highly reactive metals. This method is economical and commonly used in metallurgy for obtaining less reactive metals.
18. Why are gold and platinum called noble metals?
Answer:
Gold and platinum are called noble metals because they are highly resistant to corrosion and oxidation. They do not react easily with air, water, or most chemicals under ordinary conditions. Due to their low reactivity, they remain shiny and retain their appearance for long periods. These metals are found in nature in their free state and do not require extensive extraction processes. Their resistance to corrosion makes them valuable for jewellery, electronics, and scientific instruments. Their rarity and stability contribute to their high economic value.
19. Why is aluminium used for making cooking utensils?
Answer:
Aluminium is widely used for making cooking utensils because it possesses several useful properties. It is a good conductor of heat, allowing food to cook evenly and efficiently. Aluminium is lightweight, making utensils easy to handle. It is also resistant to corrosion because it forms a protective oxide layer on its surface. Additionally, aluminium is relatively inexpensive compared to many other metals. Its durability and ability to withstand high temperatures make it suitable for daily cooking purposes. Therefore, aluminium is one of the most commonly used metals in kitchenware.
20. Why are copper and aluminium used in electrical wiring?
Answer:
Copper and aluminium are commonly used in electrical wiring because they are excellent conductors of electricity. Their free electrons allow electric current to pass with very little resistance. Copper is preferred for household wiring due to its superior conductivity and durability. Aluminium is lighter and less expensive, making it suitable for long-distance power transmission. Both metals are ductile, allowing them to be drawn into thin wires easily. They also possess sufficient strength and resistance to corrosion, ensuring reliable performance over long periods. These properties make copper and aluminium ideal materials for electrical applications.