Uses of Metals and Non-metals - Class 10 Science

⚙️ Uses of Metals and Non-metals

Class 10 Science | Metals and Non-metals | CBSE + Foundation + Competitive

⚙️ Uses of Metals and Non-metals – धातु एवं अधातु के उपयोग

📘 1. Introduction / परिचय

English: Metals and non-metals are widely used in our daily life, industries, agriculture, medicine, construction, transportation and electrical systems. Their uses depend on their physical and chemical properties.

हिन्दी: धातु और अधातु हमारे दैनिक जीवन, उद्योग, कृषि, चिकित्सा, निर्माण, परिवहन तथा विद्युत प्रणालियों में व्यापक रूप से उपयोग किए जाते हैं। इनके उपयोग इनके भौतिक एवं रासायनिक गुणों पर निर्भर करते हैं।

🔩 2. Important Uses of Iron / लोहे के प्रमुख उपयोग

Iron (Fe) is one of the most widely used metals because it is strong, durable and relatively abundant.

लोहा (Fe) अपनी मजबूती, टिकाऊपन और उपलब्धता के कारण सबसे अधिक उपयोग की जाने वाली धातुओं में से एक है।

Use / उपयोग	Application / प्रयोग
Construction / निर्माण	Buildings, bridges and structural frameworks
Machines / मशीनें	Machine parts and industrial equipment
Tools / औजार	Various tools and implements
Transport / परिवहन	Railway tracks, vehicles and heavy structures
Steel production / इस्पात निर्माण	Iron is a major component of steel.

🔌 3. Important Uses of Copper / तांबे के प्रमुख उपयोग

Copper is widely used because it is a good conductor of electricity and heat. It is also ductile and can be drawn into wires.

तांबे का व्यापक उपयोग इसलिए किया जाता है क्योंकि यह विद्युत एवं ऊष्मा का अच्छा चालक है। यह तन्य भी है, इसलिए इससे तार बनाए जा सकते हैं।

Use / उपयोग	Reason / कारण
Electrical wiring / विद्युत तार	Excellent electrical conductivity and ductility
Electrical components / विद्युत उपकरण	Good conductor and easy to shape
Heat exchangers / ऊष्मा विनिमायक	Good thermal conductivity
Utensils / बर्तन	Good heat conduction
Alloys / मिश्रधातु	Used in brass and bronze

⚡ 4. Why is Copper Used for Electrical Wiring?

Copper is used for electrical wiring mainly because it has high electrical conductivity and relatively low electrical resistance.

तांबे का उपयोग विद्युत तारों में मुख्यतः इसकी उच्च विद्युत चालकता तथा अपेक्षाकृत कम प्रतिरोध के कारण किया जाता है।

1. Good electrical conductor: Electric current can pass through copper easily.
   अच्छा विद्युत चालक: तांबे में विद्युत धारा आसानी से प्रवाहित होती है।
2. Ductile: Copper can be drawn into thin wires.
   तन्य: तांबे से पतले तार बनाए जा सकते हैं।
3. Low resistance: It produces comparatively less electrical energy loss as heat for a given current.
   कम प्रतिरोध: समान धारा के लिए विद्युत ऊर्जा की ऊष्मा के रूप में हानि अपेक्षाकृत कम होती है।
4. Durable: Copper wiring can remain useful for a long time under suitable conditions.
   टिकाऊ: उचित परिस्थितियों में तांबे के तार लंबे समय तक उपयोगी रहते हैं।

🪶 5. Important Uses of Aluminium / एल्युमिनियम के प्रमुख उपयोग

Aluminium is light, malleable, ductile and resistant to corrosion because of its protective oxide layer.

एल्युमिनियम हल्का, आघातवर्धनीय, तन्य तथा अपनी सुरक्षात्मक ऑक्साइड परत के कारण संक्षारण के प्रति प्रतिरोधी होता है।

Use / उपयोग	Reason / कारण
Aircraft / विमान	Low density and useful strength-to-weight ratio
Electrical cables / विद्युत केबल	Good electrical conductivity and low mass
Utensils / बर्तन	Good heat conduction and low density
Packaging / पैकेजिंग	Can be made into thin sheets and is corrosion resistant
Construction / निर्माण	Lightweight structures, doors and windows

🌿 6. Important Uses of Non-metals / अधातुओं के प्रमुख उपयोग

Non-metals also play essential roles in life and industry. Their uses depend on their chemical and physical properties.

अधातु भी जीवन और उद्योग में अत्यंत महत्वपूर्ण हैं। इनके उपयोग इनके भौतिक एवं रासायनिक गुणों पर निर्भर करते हैं।

Non-metal / अधातु	Important Use / प्रमुख उपयोग
Oxygen (O₂)	Respiration and medical oxygen
Nitrogen (N₂)	Fertiliser production and food packaging
Chlorine (Cl₂)	Water purification and manufacture of chemicals
Iodine (I₂)	Antiseptic preparations and nutrition
Carbon	Fuel, graphite electrodes and many industrial applications
Sulphur	Sulphuric acid manufacture and vulcanisation of rubber
Phosphorus	Fertilisers and matches

⭐ 7. Two Important Uses of Non-metals / दो महत्वपूर्ण अधातु उपयोग

1. Oxygen: Used in respiration and medical oxygen supply.

ऑक्सीजन: श्वसन तथा चिकित्सा में ऑक्सीजन की आपूर्ति के लिए उपयोग होती है।

2. Chlorine: Used for disinfecting drinking water.

क्लोरीन: पीने के पानी को कीटाणुरहित करने के लिए उपयोग किया जाता है।

📊 8. Uses Based on Properties / गुणों के आधार पर उपयोग

Property / गुण	Material / पदार्थ	Use / उपयोग
Good electrical conductivity	Copper	Electrical wires
Low density	Aluminium	Aircraft and cables
High strength	Iron/Steel	Buildings and bridges
Good heat conductivity	Copper/Aluminium	Utensils and heat exchangers
Oxidising property	Oxygen	Respiration
Disinfecting property	Chlorine	Water purification

📝 9. 30 MCQs – Uses of Metals and Non-metals

Q1 Why is copper commonly used for electrical wiring?

A. It is a poor conductor

B. It has high electrical conductivity

C. It is a non-metal

D. It has very high resistance

Answer: B — Copper is an excellent conductor of electricity.

Q2 Which property of copper helps in making wires?

A. Brittleness

B. Malleability only

C. Ductility

D. Sonority

Answer: C — Copper can be drawn into thin wires because it is ductile.

Q3 Which metal is widely used in construction of buildings and bridges?

A. Iron/Steel

B. Mercury

C. Sodium

D. Potassium

Answer: A.

Q4 Which metal is commonly used in aircraft because of its low density?

A. Iron

B. Copper

C. Aluminium

D. Lead

Answer: C — Aluminium is lightweight.

Q5 Which non-metal is essential for respiration?

A. Oxygen

B. Sulphur

C. Phosphorus

D. Chlorine

Answer: A — Oxygen is required for aerobic respiration.

Q6 Which non-metal is commonly used to disinfect drinking water?

A. Nitrogen

B. Chlorine

C. Sulphur

D. Carbon

Answer: B — Chlorine is widely used for water disinfection.

Q7 Aluminium is suitable for making aircraft mainly because it is:

A. Very dense

B. Lightweight

C. A non-metal

D. Highly brittle

Answer: B.

Q8 Which metal is used in electrical cables because it combines good conductivity with low mass?

A. Aluminium

B. Lead

C. Mercury

D. Zinc

Answer: A.

Q9 Which property is especially important for copper wires?

A. High electrical resistance

B. High electrical conductivity

C. Brittleness

D. Low density only

Answer: B.

Q10 Iron is extensively used in machines because it can provide:

A. Useful strength and durability

B. Very low density like helium

C. Non-metallic behaviour

D. Electrical insulation

Answer: A.

Q11 Which non-metal is important in fertiliser manufacture?

A. Nitrogen

B. Gold

C. Copper

D. Aluminium

Answer: A.

Q12 Which element is widely used in the manufacture of sulphuric acid?

A. Sulphur

B. Copper

C. Aluminium

D. Iron

Answer: A.

Q13 Which property of aluminium protects it from rapid corrosion?

A. Formation of a protective oxide layer

B. Complete absence of reaction with oxygen

C. High density

D. Poor conductivity

Answer: A.

Q14 Which metal is commonly used for making cooking utensils due to good heat conductivity?

A. Copper

B. Sodium

C. Potassium

D. Mercury

Answer: A.

Q15 Which non-metal is used in some antiseptic preparations?

A. Iodine

B. Nitrogen

C. Oxygen only

D. Sulphur only

Answer: A.

Q16 Which metal is an important component of steel?

A. Iron

B. Chlorine

C. Sulphur

D. Phosphorus

Answer: A.

Q17 Why can aluminium be used for making thin sheets?

A. It is malleable

B. It is brittle

C. It is a gas

D. It is a poor conductor

Answer: A — Aluminium is malleable.

Q18 Which non-metal is present in the air and is essential for plant growth through fertiliser production?

A. Nitrogen

B. Gold

C. Copper

D. Iron

Answer: A.

Q19 Which metal is suitable for making railway tracks and heavy structures?

A. Iron/Steel

B. Sodium

C. Mercury

D. Potassium

Answer: A.

Q20 Which property of copper is responsible for its use in heat exchangers?

A. Poor thermal conductivity

B. Good thermal conductivity

C. Brittleness

D. Very high density only

Answer: B.

Q21 Which non-metal is commonly used for water purification?

A. Chlorine

B. Carbon dioxide

C. Sulphur

D. Phosphorus

Answer: A.

Q22 Which metal is widely used for making machine parts?

A. Iron

B. Chlorine

C. Oxygen

D. Nitrogen

Answer: A.

Q23 Which property makes copper suitable for electrical wires?

A. Electrical insulation

B. Electrical conductivity and ductility

C. Brittleness

D. Very high resistance

Answer: B.

Q24 Which non-metal is used in rubber vulcanisation?

A. Sulphur

B. Oxygen

C. Nitrogen

D. Chlorine

Answer: A.

Q25 Which metal is preferred where low weight is important?

A. Aluminium

B. Lead

C. Mercury

D. Iron

Answer: A.

Q26 Which element is commonly used in match-related applications?

A. Phosphorus

B. Aluminium

C. Copper

D. Iron

Answer: A.

Q27 Which material is widely used for structural frameworks?

A. Steel

B. Oxygen

C. Chlorine

D. Nitrogen

Answer: A.

Q28 Which property of iron/steel makes it useful in bridges?

A. Strength

B. Electrical insulation

C. Very low density

D. Gas-like nature

Answer: A.

Q29 Which pair is correctly matched?

A. Copper — electrical wiring

B. Chlorine — railway tracks

C. Iron — medical oxygen

D. Aluminium — water disinfection

Answer: A.

Q30 The use of a metal or non-metal mainly depends upon its:

A. Properties

B. Name only

C. Atomic symbol only

D. Colour only

Answer: A — Applications depend mainly on useful physical and chemical properties.

✍️ 10. 30 Subjective Questions with Answers

1 Mark Q1. Give one important use of iron. / लोहे का एक प्रमुख उपयोग लिखिए।

Answer: Iron/steel is used in construction of buildings and bridges.
हिन्दी: लोहे/इस्पात का उपयोग भवनों और पुलों के निर्माण में किया जाता है।

1 Mark Q2. Give one important use of copper.

Answer: Copper is used for electrical wiring.

1 Mark Q3. Give one important use of aluminium.

Answer: Aluminium is used in aircraft and electrical cables.

1 Mark Q4. Name one non-metal used for water purification.

Answer: Chlorine.
हिन्दी: क्लोरीन।

1 Mark Q5. Name the non-metal essential for respiration.

Answer: Oxygen.

2 Marks Q6. Give two uses of iron.

Answer:
1. Construction of buildings and bridges.
2. Manufacture of machines, tools and railway tracks.

2 Marks Q7. Give two uses of copper.

Answer:
1. Electrical wiring.
2. Heat exchangers and utensils.

2 Marks Q8. Give two uses of aluminium.

Answer:
1. Aircraft manufacturing.
2. Electrical cables and packaging.

2 Marks Q9. Give two important uses of non-metals.

Answer:
1. Oxygen is used in respiration and medical applications.
2. Chlorine is used for disinfecting drinking water.

2 Marks Q10. Why is copper used for electrical wiring?

Answer: Copper has high electrical conductivity and is ductile, so it can be drawn into thin wires.

3 Marks Q11. Explain three uses of iron.

Answer:
1. Construction of buildings and bridges.
2. Manufacture of machines and tools.
3. Railway tracks and heavy engineering structures.

3 Marks Q12. Explain three uses of copper.

Answer:
1. Electrical wiring because of high conductivity.
2. Heat exchangers because of good thermal conductivity.
3. Manufacture of alloys such as brass and bronze.

3 Marks Q13. Explain three uses of aluminium.

Answer:
1. Aircraft because it is lightweight.
2. Electrical cables because it is conductive and light.
3. Utensils and packaging because it is malleable and corrosion resistant.

3 Marks Q14. Why is aluminium used in aircraft?

Answer: Aluminium has low density, is easy to form and provides a useful strength-to-weight ratio. It also has good corrosion resistance.

3 Marks Q15. Why is copper suitable for making wires?

Answer:
1. It has high electrical conductivity.
2. It has relatively low electrical resistance.
3. It is ductile and can be drawn into thin wires.

4 Marks Q16. Explain four uses of metals based on their properties.

Answer:
1. Copper → electrical wires due to high conductivity.
2. Aluminium → aircraft due to low density.
3. Iron/steel → buildings due to strength.
4. Copper/aluminium → utensils due to good thermal conductivity.

4 Marks Q17. Explain four important uses of non-metals.

Answer:
1. Oxygen → respiration and medical oxygen.
2. Nitrogen → fertiliser manufacture.
3. Chlorine → water disinfection.
4. Sulphur → sulphuric acid manufacture and rubber vulcanisation.

4 Marks Q18. Explain why the properties of metals determine their uses.

Answer: Metals are selected according to properties required for a particular application. High conductivity makes copper suitable for wires, low density makes aluminium useful in aircraft, and high strength makes iron/steel useful in construction.

4 Marks Q19. Compare the uses of copper and aluminium in electrical applications.

Answer:
Copper: High conductivity and excellent ductility make it widely used for electrical wiring.

Aluminium: It also conducts electricity and is much lighter, so it is useful for overhead electrical cables where low weight is advantageous.

4 Marks Q20. Explain two uses each of iron, copper and aluminium.

Iron: Construction and machinery.
Copper: Electrical wiring and heat exchangers.
Aluminium: Aircraft and electrical cables.

5 Marks Q21. Explain the important uses of iron in daily life and industry.

Answer:
Iron and iron-based materials are used in:
1. Buildings and bridges.
2. Railway tracks.
3. Machines and machine parts.
4. Tools and equipment.
5. Vehicles and other engineering structures.

5 Marks Q22. Explain the important uses of copper and the properties responsible for these uses.

Answer:
1. Electrical wires → high electrical conductivity and ductility.
2. Heat exchangers → good thermal conductivity.
3. Utensils → good thermal conductivity.
4. Electrical components → good conductivity and easy shaping.
5. Alloys → copper forms useful alloys such as brass and bronze.

5 Marks Q23. Explain the important uses of aluminium and the properties responsible for these uses.

Answer:
1. Aircraft → low density.
2. Electrical cables → conductivity with low mass.
3. Packaging → malleability and corrosion resistance.
4. Utensils → good heat conductivity and low density.
5. Doors/windows → lightweight and corrosion resistant.

5 Marks Q24. Why are non-metals important even though they generally do not show typical metallic properties?

Answer: Non-metals have important chemical properties and perform essential functions. Oxygen supports respiration, nitrogen is important for fertilisers, chlorine disinfects water, sulphur is used in industrial processes and phosphorus is used in fertilisers and matches.

5 Marks Q25. Explain the relationship between physical properties and uses of metals.

Answer:
The use of a metal is selected according to its properties:
• Conductivity → copper for wires.
• Ductility → copper for thin wires.
• Low density → aluminium for aircraft.
• Strength → iron/steel for buildings and bridges.
• Thermal conductivity → copper/aluminium for utensils.

6 Marks Q26. Give a detailed account of the uses of iron, copper and aluminium.

Answer:
Iron: Used in buildings, bridges, railway tracks, machines, tools and vehicles because of its strength and durability.

Copper: Used in electrical wiring, electrical components, heat exchangers and utensils because of its excellent electrical and thermal conductivity and ductility.

Aluminium: Used in aircraft, electrical cables, utensils, packaging and construction because it is lightweight, malleable and corrosion resistant.

6 Marks Q27. Explain why copper is preferred for electrical wiring. What properties make it suitable?

Answer:
Copper is preferred for many electrical wiring applications because:
1. It has high electrical conductivity.
2. It has relatively low electrical resistance.
3. It is ductile.
4. It can be drawn into thin wires.
5. It is durable under suitable conditions.
6. Its connections can be made reliably using appropriate electrical techniques.

6 Marks Q28. Describe important uses of non-metals with examples.

Answer:
1. Oxygen → respiration and medical oxygen.
2. Nitrogen → fertiliser production and food packaging.
3. Chlorine → drinking-water disinfection.
4. Iodine → antiseptic preparations and nutrition.
5. Sulphur → sulphuric acid manufacture and rubber vulcanisation.
6. Phosphorus → fertilisers and match-related applications.

6 Marks Q29. How are the uses of metals and non-metals different?

Answer:
Metals are commonly used where properties such as strength, electrical conductivity, thermal conductivity, ductility and malleability are required.

Non-metals are widely used because of their chemical properties and specific physical properties. Oxygen is needed for respiration, nitrogen is used in fertilisers, chlorine is used for water disinfection and sulphur is important in industrial processes.

Thus, the application depends on the particular useful property of the material.

6 Marks Q30. “The use of a substance depends on its properties.” Justify with suitable examples.

Answer:
The statement is correct.

Examples:
1. Copper is used in wires because it conducts electricity well and is ductile.
2. Aluminium is used in aircraft because it is lightweight and corrosion resistant.
3. Iron/steel is used in buildings because of its strength and durability.
4. Oxygen is used in respiration because it supports the life-sustaining oxidation process.
5. Chlorine is used in water treatment because it has disinfecting properties.
6. Sulphur is used in rubber vulcanisation because of its ability to form cross-links in rubber.

🚀 11. Quick Revision / त्वरित पुनरावृत्ति

Iron / लोहा → Buildings, bridges, railway tracks, machines, tools.

Copper / तांबा → Electrical wires, electrical components, heat exchangers, utensils.

Aluminium / एल्युमिनियम → Aircraft, electrical cables, packaging, utensils, doors/windows.

Oxygen / ऑक्सीजन → Respiration and medical oxygen.

Nitrogen / नाइट्रोजन → Fertilisers and food packaging.

Chlorine / क्लोरीन → Water disinfection.

Sulphur / सल्फर → Sulphuric acid manufacture and rubber vulcanisation.

🎯 CBSE Exam Tip:

Remember the property → use relationship:

High electrical conductivity → Copper → Electrical wires
Ductility → Copper → Wires
Low density → Aluminium → Aircraft
High strength → Iron/Steel → Buildings & Bridges
Disinfecting property → Chlorine → Water purification
Respiration → Oxygen → Life processes

Alloys - Class 10 Science

⚗️ Alloys

Class 10 Science | Metals and Non-metals | CBSE + Foundation + Competitive

⚙️ Alloys – मिश्रधातु

📘 1. What is an Alloy? / मिश्रधातु क्या है?

English: An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal, prepared to obtain desirable properties.

हिन्दी: मिश्रधातु (Alloy) दो या दो से अधिक धातुओं अथवा किसी धातु और अधातु का समांगी मिश्रण होती है, जिसे वांछित गुण प्राप्त करने के लिए बनाया जाता है।

Important:
Alloys are generally made by melting the constituent elements together in suitable proportions and then cooling the mixture.

महत्वपूर्ण:
मिश्रधातु सामान्यतः इसके घटकों को उचित अनुपात में पिघलाकर और फिर ठंडा करके बनाई जाती है।

🎯 2. Why are Alloys Made? / मिश्रधातुएँ क्यों बनाई जाती हैं?

Pure metals may not always possess all the properties required for a particular use. Therefore, other elements are added to modify their properties.

शुद्ध धातुओं में किसी विशेष उपयोग के लिए आवश्यक सभी गुण हमेशा नहीं होते। इसलिए उनके गुणों को बदलने या सुधारने के लिए दूसरी धातु या अधातु मिलाई जाती है।

Purpose / उद्देश्य	Explanation / व्याख्या
Increase hardness / कठोरता बढ़ाना	Alloying can make a metal harder and stronger.
Increase strength / मजबूती बढ़ाना	Some alloys can withstand greater mechanical stress.
Prevent corrosion / संक्षारण रोकना	Certain alloys have better resistance to corrosion.
Change melting point / गलनांक बदलना	Alloying can increase or decrease the melting point.
Improve appearance / रूप सुधारना	Some alloys have better colour and shine.
Improve electrical properties / विद्युत गुण सुधारना	Some alloys have useful electrical resistance.

⭐ 3. Important Properties of Alloys / मिश्रधातुओं के प्रमुख गुण

1. Hardness: Many alloys are harder than pure metals.
   कठोरता: कई मिश्रधातुएँ शुद्ध धातुओं से अधिक कठोर होती हैं।
2. Strength: Alloying can improve mechanical strength.
   मजबूती: मिश्रधातु बनाने से यांत्रिक मजबूती बढ़ सकती है।
3. Corrosion resistance: Some alloys resist corrosion better than their constituent metals.
   संक्षारण प्रतिरोध: कुछ मिश्रधातुएँ अपने घटक धातुओं की तुलना में संक्षारण से अधिक सुरक्षित रहती हैं।
4. Controlled melting point: Alloy composition can modify melting behaviour.
   नियंत्रित गलनांक: संघटन बदलकर गलनांक के गुणों को बदला जा सकता है।

🔬 4. Important Examples of Alloys and Their Uses

Alloy / मिश्रधातु	Composition / संघटन	Uses / उपयोग
Brass / पीतल	Copper + Zinc तांबा + जस्ता	Utensils, screws, musical instruments, decorative items
Bronze / कांसा	Copper + Tin तांबा + टिन	Statues, medals, bells, bearings
Solder / सोल्डर	Lead + Tin सीसा + टिन	Joining electrical wires and components
Stainless Steel / स्टेनलेस स्टील	Iron + Chromium + Nickel (commonly)	Utensils, surgical instruments, kitchen equipment
Steel / स्टील	Iron + Carbon	Buildings, bridges, machines, tools
Amalgam / अमलगम	Mercury + another metal	Used in specialised applications

🟡 5. Brass / पीतल

Brass is mainly an alloy of copper and zinc.

पीतल मुख्यतः तांबा और जस्ता की मिश्रधातु है।

It is commonly used for screws, taps, utensils, musical instruments and decorative articles.

इसका उपयोग स्क्रू, नल, बर्तन, संगीत वाद्ययंत्र तथा सजावटी वस्तुओं में किया जाता है।

🟤 6. Bronze / कांसा

Bronze is an alloy mainly containing copper and tin.

कांसा मुख्यतः तांबा और टिन की मिश्रधातु है।

It is hard and is used for statues, medals, bells and bearings.

⚙️ 7. Stainless Steel / स्टेनलेस स्टील

Stainless steel is an alloy based mainly on iron with chromium and often nickel and other elements.

स्टेनलेस स्टील मुख्यतः लोहे पर आधारित मिश्रधातु है जिसमें क्रोमियम तथा प्रायः निकेल और अन्य तत्व होते हैं।

Chromium helps in providing good corrosion resistance by forming a thin protective oxide layer on the surface.

क्रोमियम सतह पर एक पतली सुरक्षात्मक ऑक्साइड परत बनाने में सहायता करता है, जिससे संक्षारण प्रतिरोध बढ़ता है।

🔌 8. Solder / सोल्डर

Solder is traditionally a low-melting alloy of lead and tin.

सोल्डर पारंपरिक रूप से सीसा और टिन की कम गलनांक वाली मिश्रधातु है।

Its low melting point makes it useful for joining metal surfaces, especially in electrical and electronic work.

इसके कम गलनांक के कारण इसका उपयोग धातु की सतहों को जोड़ने, विशेषकर विद्युत एवं इलेक्ट्रॉनिक कार्यों में किया जाता है।

🧪 9. Why is Pure Gold Alloyed? / शुद्ध सोने में मिश्रधातु क्यों बनाई जाती है?

Pure gold is very soft and is not suitable for making durable jewellery. Therefore, it is alloyed with other metals to increase its hardness and strength.

शुद्ध सोना बहुत नरम होता है और टिकाऊ आभूषण बनाने के लिए उपयुक्त नहीं होता। इसलिए इसकी कठोरता और मजबूती बढ़ाने के लिए इसमें अन्य धातुएँ मिलाई जाती हैं।

Example: Jewellery gold is commonly alloyed with metals such as copper or silver.

उदाहरण: आभूषणों में प्रयुक्त सोने में सामान्यतः तांबा या चाँदी जैसी धातुएँ मिलाई जाती हैं।

📌 10. Important Exam Points / महत्वपूर्ण परीक्षा बिंदु

• Alloy: Homogeneous mixture of two or more metals or a metal and a non-metal.
• Brass: Copper + Zinc.
• Bronze: Copper + Tin.
• Steel: Iron + Carbon.
• Stainless steel: Iron-based alloy containing chromium and often nickel.
• Alloys are made to improve useful properties such as hardness, strength and corrosion resistance.
• Pure gold is soft; alloying makes it harder and more suitable for jewellery.

📝 11. 30 MCQs – Alloys / मिश्रधातु बहुविकल्पीय प्रश्न

Q1 What is an alloy? / मिश्रधातु क्या है?

A. A homogeneous mixture of metals or a metal and non-metal

B. A pure metal

C. A compound containing only oxygen

D. A non-metallic element

Answer: A — Alloy is generally a homogeneous mixture of two or more metals or a metal and a non-metal.

Q2 Brass is an alloy of which metals? / पीतल किन धातुओं की मिश्रधातु है?

A. Iron and carbon

B. Copper and zinc

C. Copper and tin

D. Lead and tin

Answer: B — Brass = Copper + Zinc.

Q3 Bronze mainly contains:

A. Copper and zinc

B. Iron and carbon

C. Copper and tin

D. Lead and mercury

Answer: C — Bronze mainly contains copper and tin.

Q4 Which alloy is commonly used for making electrical joints?

A. Bronze

B. Brass

C. Steel

D. Solder

Answer: D — Solder is used for joining metal/electrical components.

Q5 Why are alloys made?

A. To improve desirable properties

B. To remove all metals

C. To make metals radioactive

D. To convert metals into gases

Answer: A — Alloying modifies properties such as hardness, strength and corrosion resistance.

Q6 Steel is mainly an alloy of:

A. Copper and zinc

B. Iron and carbon

C. Copper and tin

D. Tin and lead

Answer: B — Steel is primarily iron with carbon.

Q7 Which alloy is known for good corrosion resistance?

A. Stainless steel

B. Solder

C. Brass only

D. Lead-tin only

Answer: A — Stainless steel has good corrosion resistance.

Q8 Which element in stainless steel strongly contributes to corrosion resistance?

A. Carbon

B. Lead

C. Chromium

D. Mercury

Answer: C — Chromium forms a protective oxide layer.

Q9 Pure gold is alloyed mainly because it is:

A. Very hard

B. Very soft

C. Highly magnetic

D. Non-metallic

Answer: B — Pure gold is very soft.

Q10 Which alloy contains copper and zinc?

A. Bronze

B. Brass

C. Steel

D. Solder

Answer: B — Brass contains copper and zinc.

Q11 Which alloy contains copper and tin?

A. Bronze

B. Brass

C. Steel

D. Solder

Answer: A — Bronze = Copper + Tin.

Q12 Alloying can generally increase the:

A. Hardness

B. Atomic number

C. Number of protons

D. Nuclear charge

Answer: A — Alloying can improve hardness.

Q13 Which alloy is widely used for utensils?

A. Stainless steel

B. Solder

C. Amalgam

D. Nichrome only

Answer: A — Stainless steel is widely used for utensils.

Q14 The main purpose of adding chromium to steel is to improve:

A. Radioactivity

B. Corrosion resistance

C. Density only

D. Electrical charge

Answer: B — Chromium improves corrosion resistance.

Q15 Which alloy was traditionally used for joining electrical wires?

A. Bronze

B. Brass

C. Solder

D. Steel

Answer: C — Solder is used for joining electrical components.

Q16 Which property is NOT generally the purpose of alloying?

A. Increasing hardness

B. Improving corrosion resistance

C. Changing melting behaviour

D. Increasing atomic number of the metal

Answer: D — Atomic number cannot be changed by ordinary alloying.

Q17 An alloy is generally prepared by:

A. Freezing gases

B. Melting constituents and mixing them

C. Burning all components

D. Dissolving only in water

Answer: B.

Q18 Which alloy is commonly used for statues and medals?

A. Bronze

B. Solder

C. Steel

D. Amalgam

Answer: A — Bronze.

Q19 Which one is an iron-based alloy?

A. Brass

B. Bronze

C. Stainless steel

D. Solder

Answer: C — Stainless steel is iron-based.

Q20 Alloying can make a metal:

A. More useful for a particular application

B. Always radioactive

C. Always gaseous

D. Always non-metallic

Answer: A.

Q21 Which alloy is mainly used for decorative articles and musical instruments?

A. Brass

B. Solder

C. Steel

D. Amalgam

Answer: A — Brass.

Q22 Which alloy is traditionally associated with lead and tin?

A. Brass

B. Bronze

C. Solder

D. Steel

Answer: C — Solder.

Q23 Why is stainless steel preferred for kitchen utensils?

A. It is highly radioactive

B. It has good corrosion resistance

C. It melts at room temperature

D. It is a non-metal

Answer: B.

Q24 Which statement about alloys is correct?

A. All alloys are compounds

B. All alloys contain only non-metals

C. Alloys are mixtures with modified properties

D. All alloys are gases

Answer: C.

Q25 Which of the following is NOT an alloy?

A. Brass

B. Bronze

C. Stainless steel

D. Copper

Answer: D — Copper is an element, not an alloy.

Q26 Alloying may alter the:

A. Hardness and strength

B. Number of protons

C. Atomic identity of each element

D. Nuclear structure

Answer: A.

Q27 Which alloy is particularly useful where corrosion resistance is required?

A. Stainless steel

B. Solder

C. Lead only

D. Pure iron

Answer: A.

Q28 The protective layer on stainless steel is mainly associated with:

A. Chromium oxide

B. Sodium chloride

C. Calcium carbonate

D. Copper sulphate

Answer: A — Chromium oxide.

Q29 Which property makes solder useful for joining components?

A. Very high melting point

B. Relatively low melting point

C. Radioactivity

D. Very high density only

Answer: B.

Q30 The best reason for making alloys is:

A. To obtain improved or desired properties

B. To change the nucleus of atoms

C. To eliminate all metals

D. To produce only gases

Answer: A.

✍️ 12. 30 Subjective Questions with Answers / वर्णनात्मक प्रश्न

1 Mark Q1. What is an alloy? / मिश्रधातु क्या है?

Answer: An alloy is a homogeneous mixture of two or more metals or a metal and a non-metal.
हिन्दी: मिश्रधातु दो या अधिक धातुओं या धातु-अधातु का समांगी मिश्रण है।

1 Mark Q2. Give one example of an alloy.

Answer: Brass.
हिन्दी: पीतल।

1 Mark Q3. Name the constituents of brass.

Answer: Copper and zinc.
हिन्दी: तांबा और जस्ता।

1 Mark Q4. Name the constituents of bronze.

Answer: Copper and tin.
हिन्दी: तांबा और टिन।

1 Mark Q5. Why is pure gold not commonly used for making durable jewellery?

Answer: Pure gold is very soft, so it is alloyed to increase hardness and strength.

2 Marks Q6. Why are alloys made? Give two reasons.

Answer:
1. To increase hardness and strength.
2. To improve corrosion resistance or modify melting behaviour.

हिन्दी: मिश्रधातुएँ कठोरता, मजबूती तथा संक्षारण प्रतिरोध जैसे गुणों को सुधारने के लिए बनाई जाती हैं।

2 Marks Q7. What is brass? Mention one use.

Answer: Brass is an alloy of copper and zinc. It is used in taps, screws, utensils and musical instruments.

2 Marks Q8. What is bronze? Mention one use.

Answer: Bronze is mainly an alloy of copper and tin. It is used for statues, medals and bells.

2 Marks Q9. Why is stainless steel preferred over ordinary iron for utensils?

Answer: Stainless steel has better corrosion resistance and is durable, making it suitable for utensils.

2 Marks Q10. What is solder and why is it useful?

Answer: Solder is traditionally a lead-tin alloy. Its relatively low melting point makes it useful for joining metal and electrical components.

3 Marks Q11. Explain three advantages of alloying.

Answer:
1. Increases hardness.
2. Increases strength.
3. Improves corrosion resistance.

3 Marks Q12. Write three examples of alloys with their compositions.

Answer:
1. Brass = Copper + Zinc.
2. Bronze = Copper + Tin.
3. Steel = Iron + Carbon.

3 Marks Q13. Why are alloys generally preferred for engineering applications?

Answer: Alloys can have improved hardness, strength, wear resistance and corrosion resistance compared with pure metals.

3 Marks Q14. Explain why pure gold is alloyed.

Answer: Pure gold is very soft. Adding suitable metals increases its hardness and strength, making it more suitable for jewellery and other applications.

3 Marks Q15. Explain the role of chromium in stainless steel.

Answer: Chromium reacts with oxygen at the surface and helps form a thin, adherent chromium oxide layer. This protective layer reduces further corrosion.

4 Marks Q16. Differentiate between a pure metal and an alloy.

Pure Metal	Alloy
Contains one principal metallic element.	Contains two or more elements, usually metals or metal + non-metal.
Has properties characteristic of that metal.	Properties can be modified by changing composition.
May be softer or less corrosion resistant.	Often has improved hardness, strength or corrosion resistance.

4 Marks Q17. Explain four uses of alloys with examples.

Answer:
1. Brass → taps, screws and musical instruments.
2. Bronze → statues, medals and bells.
3. Stainless steel → utensils and surgical instruments.
4. Steel → buildings, bridges, machines and tools.

4 Marks Q18. Explain why alloys have different properties from pure metals.

Answer: Atoms of different elements have different sizes and bonding characteristics. Their presence disturbs the regular arrangement of atoms in the pure metal. This can change properties such as hardness, strength, electrical resistance and melting behaviour.

4 Marks Q19. Explain the importance of stainless steel in daily life.

Answer: Stainless steel is strong, durable and resistant to corrosion. Therefore it is widely used in kitchen utensils, cutlery, medical instruments, appliances and industrial equipment.

4 Marks Q20. Explain brass and bronze with composition and uses.

Answer:
Brass: Copper + Zinc; used in taps, screws and musical instruments.
Bronze: Copper + Tin; used in statues, medals and bells.

5 Marks Q21. Explain the concept of alloying in detail.

Answer:
Alloying is the process of combining two or more elements, usually metals or a metal and a non-metal, to obtain improved properties.

The main purposes are:
1. Increasing hardness.
2. Increasing strength.
3. Improving corrosion resistance.
4. Modifying melting behaviour.
5. Improving suitability for a particular application.

5 Marks Q22. Describe five important alloys and their uses.

Answer:
1. Brass → Copper + Zinc → taps, screws and instruments.
2. Bronze → Copper + Tin → statues and medals.
3. Steel → Iron + Carbon → buildings and machines.
4. Stainless steel → Iron + Chromium + other elements → utensils and medical instruments.
5. Solder → traditionally Lead + Tin → joining electrical components.

5 Marks Q23. Why are pure metals not always suitable for practical applications?

Answer: Pure metals may be too soft, weak or susceptible to corrosion for certain applications. Alloying allows their properties to be modified so that they become harder, stronger, more durable or more corrosion resistant.

5 Marks Q24. Explain the importance of alloys in modern technology.

Answer: Alloys are important because their properties can be tailored for specific applications. They are used in construction, transportation, electrical work, medical instruments, machinery, utensils and jewellery. Their improved strength, hardness and corrosion resistance make them more useful than many pure metals.

5 Marks Q25. Explain why alloying can improve corrosion resistance.

Answer: Alloying can introduce elements that form stable protective layers or change the chemical behaviour of the material. For example, chromium in stainless steel helps form a protective chromium oxide layer, which reduces further corrosion.

6 Marks Q26. Explain alloys, their preparation, advantages and examples.

Answer:
Definition: An alloy is a homogeneous mixture of two or more metals or a metal and a non-metal.

Preparation: The constituents are generally melted together in suitable proportions and then cooled.

Advantages:
1. Greater hardness.
2. Greater strength.
3. Better corrosion resistance.
4. Modified melting behaviour.
5. Better suitability for particular applications.

Examples: Brass, bronze, steel, stainless steel and solder.

6 Marks Q27. Compare brass, bronze and stainless steel.

Alloy	Composition	Major Uses
Brass	Copper + Zinc	Taps, screws, instruments
Bronze	Copper + Tin	Statues, medals, bells
Stainless Steel	Iron + Chromium + often Nickel	Utensils, medical instruments, equipment

6 Marks Q28. Explain why alloys are important in construction and engineering.

Answer: Engineering materials must often withstand stress, wear and environmental conditions. Alloys can provide higher strength, hardness, durability and corrosion resistance. Steel is therefore widely used in buildings, bridges, machines and tools, while specialised alloys are used where particular combinations of properties are required.

6 Marks Q29. A student says, “Alloys are compounds.” Is the statement correct? Explain.

Answer: The statement is not generally correct. Alloys are generally mixtures of elements rather than single chemical compounds. Their composition can often vary within a range, and their properties depend on the proportions and nature of the constituent elements.

6 Marks Q30. Explain why stainless steel is preferred for many household and medical applications.

Answer:
Stainless steel is preferred because:
1. It has good corrosion resistance.
2. It has good mechanical strength.
3. It is durable.
4. It can be cleaned easily.
5. It is suitable for many food-contact applications.
6. It is useful for many medical and industrial instruments.

🚀 13. Quick Revision / त्वरित पुनरावृत्ति

Alloy → Mixture of elements, usually metals or metal + non-metal.

Brass → Copper + Zinc

Bronze → Copper + Tin

Steel → Iron + Carbon

Stainless Steel → Iron + Chromium + often Nickel

Solder → Traditionally Lead + Tin

Main purpose of alloying → Improve useful properties such as hardness, strength and corrosion resistance.

🎯 CBSE Exam Tip:
Remember these three very important pairs:

Brass = Cu + Zn
Bronze = Cu + Sn
Steel = Fe + C

Prevention of Corrosion - Class 10 Science

🛡️ Prevention of Corrosion

Class 10 Science | Metals and Non-metals | CBSE + Foundation + Competitive

🛡️ Prevention of Corrosion / संक्षारण की रोकथाम

1. What is Prevention of Corrosion? / संक्षारण की रोकथाम क्या है?

English:
Corrosion can damage metals and reduce their strength and useful life. Therefore, methods are used to prevent the contact of metal with oxygen, moisture and other corrosive substances. The main methods include:

• Painting
• Oiling and greasing
• Galvanisation
• Electroplating
• Alloying
• Cathodic protection

हिन्दी:
धातुओं को ऑक्सीजन, नमी तथा अन्य संक्षारक पदार्थों के संपर्क से बचाकर संक्षारण को रोका जा सकता है। इसके लिए पेंटिंग, तेल/ग्रीस लगाना, गैल्वनीकरण, विद्युत लेपन, मिश्रधातु निर्माण तथा कैथोडिक संरक्षण जैसी विधियों का उपयोग किया जाता है।

2. How Can Corrosion Be Prevented? / संक्षारण को कैसे रोका जा सकता है?

Method / विधि	How it prevents corrosion / कैसे रोकती है
Painting / पेंटिंग	Forms a protective barrier against air and moisture.
Oiling & Greasing / तेल एवं ग्रीस	Prevents contact with oxygen and moisture.
Galvanisation / गैल्वनीकरण	Coats iron with zinc.
Electroplating / विद्युत लेपन	Deposits a protective metal layer on another metal.
Alloying / मिश्रधातु निर्माण	Improves resistance to corrosion.

3. What is Galvanisation? / गैल्वनीकरण क्या है?

English:
Galvanisation is the process of coating iron or steel with a thin layer of zinc to protect it from corrosion. The zinc coating acts as a barrier between iron and the environment. Hindi:
लोहे या स्टील पर जिंक की पतली परत चढ़ाकर उसे संक्षारण से बचाने की प्रक्रिया को गैल्वनीकरण (Galvanisation) कहते हैं। इसमें जिंक की परत लोहे को वायु और नमी के सीधे संपर्क से बचाती है।

Iron/Steel + Zinc Coating → Protection from Corrosion

4. Why is Zinc Used in Galvanisation? / गैल्वनीकरण में जिंक का उपयोग क्यों?

Zinc is more reactive than iron. If the zinc coating is scratched, zinc can undergo oxidation preferentially and can provide sacrificial protection to the exposed iron under suitable conditions. Therefore, galvanisation can continue to protect iron even when a small area of coating is damaged.

⭐ Important CBSE Point:
Galvanisation is different from painting. Painting: Mainly provides a physical barrier. Galvanisation: Zinc provides a protective coating and can also offer sacrificial protection if the coating is damaged.

5. How Does Painting Prevent Rusting? / पेंटिंग जंग लगने से कैसे रोकती है?

English:
Paint forms a continuous protective layer over the iron surface. This layer prevents oxygen and moisture from directly reaching the iron surface. Since oxygen and moisture are required for ordinary rusting, the paint reduces the possibility of rust formation.

हिन्दी:
पेंट लोहे की सतह पर एक सुरक्षात्मक परत बना देता है। यह परत ऑक्सीजन और नमी को लोहे की सतह तक पहुँचने से रोकती है। चूँकि सामान्य रूप से जंग लगने के लिए ऑक्सीजन और नमी दोनों आवश्यक हैं, इसलिए पेंटिंग जंग लगने को रोकती है।

Iron Surface + Paint Layer → No Direct Contact with Air & Moisture

6. Important Methods of Corrosion Prevention / संक्षारण रोकने की प्रमुख विधियाँ

1. Painting: Used for gates, bridges, railings and metal structures.

2. Oiling and Greasing: Used for machine parts, tools and moving components.

3. Galvanisation: Used for iron sheets, pipes, wires and many steel products.

4. Electroplating: A protective metal coating is deposited using electrolysis.

5. Alloying: Certain alloy compositions improve corrosion resistance.

6. Cathodic Protection: The metal to be protected is made the cathode of an electrochemical system.

7. Why Should Paint Be Reapplied? / पेंट को दोबारा क्यों लगाया जाता है?

If the paint layer gets scratched, cracked or peeled off, the exposed iron can come into contact with oxygen and moisture. Therefore, damaged paint should be repaired or reapplied.

Damaged Paint → Exposed Iron → Oxygen + Moisture → Rusting

8. Galvanisation vs Painting / गैल्वनीकरण एवं पेंटिंग में अंतर

Painting	Galvanisation
Paint is applied on the surface.	Zinc coating is applied to iron/steel.
Mainly acts as a barrier.	Acts as barrier and can provide sacrificial protection.
Damaged paint exposes iron.	Zinc can protect exposed iron under suitable conditions.
Requires periodic maintenance.	Zinc coating can provide relatively durable protection.

9. 30 MCQs / बहुविकल्पीय प्रश्न

Q1. Which of the following is a method of preventing corrosion?
संक्षारण रोकने की विधि कौन-सी है?

A. Painting

B. Scratching

C. Heating iron in air

D. Keeping iron wet

Answer: A

Q2. Galvanisation involves coating iron with:

A. Copper

B. Zinc

C. Silver

D. Aluminium oxide

Answer: B

Q3. The main purpose of painting iron is to:

A. Increase its melting point

B. Prevent contact with air and moisture

C. Make it magnetic

D. Increase its density

Answer: B

Q4. Which metal is used for galvanising iron?

A. Zinc

B. Gold

C. Silver

D. Mercury

Answer: A

Q5. Galvanisation protects iron mainly by:

A. Coating it with zinc

B. Melting the iron

C. Removing all oxygen from air

D. Converting iron into copper

Answer: A

Q6. Which substance is commonly used to protect machine parts from corrosion?

A. Water

B. Oil or grease

C. Salt

D. Acid

Answer: B

Q7. Painting prevents rusting by preventing contact between iron and:

A. Oxygen and moisture

B. Nitrogen only

C. Hydrogen only

D. Carbon only

Answer: A

Q8. Zinc is used for galvanisation because it:

A. Is less reactive than gold

B. Provides a protective coating and can offer sacrificial protection

C. Always dissolves immediately

D. Is a non-metal

Answer: B

Q9. Which method is especially suitable for protecting iron sheets?

A. Galvanisation

B. Soaking in water

C. Heating in oxygen

D. Adding salt

Answer: A

Q10. Which of the following does NOT prevent corrosion?

A. Oiling

B. Painting

C. Galvanisation

D. Keeping iron continuously wet

Answer: D

Q11. The protective layer in galvanisation is made of:

A. Zinc

B. Iron

C. Carbon

D. Sulphur

Answer: A

Q12. If paint on an iron gate is scratched deeply:

A. Iron becomes completely immune to corrosion

B. Exposed iron can start corroding

C. Iron becomes gold

D. Rusting becomes impossible

Answer: B

Q13. Which method uses a protective metal coating?

A. Galvanisation

B. Drying

C. Cutting

D. Heating

Answer: A

Q14. Which method can provide sacrificial protection to iron?

A. Galvanisation with zinc

B. Painting with water

C. Washing with acid

D. Heating with oxygen

Answer: A

Q15. Corrosion can be prevented by:

A. Isolating the metal from corrosive agents

B. Increasing moisture

C. Adding salt water

D. Exposing metal to humid air

Answer: A

Q16. Oiling and greasing prevent corrosion by:

A. Creating a protective barrier

B. Producing oxygen

C. Producing rust

D. Increasing humidity

Answer: A

Q17. Which process deposits a metal coating using electricity?

A. Electroplating

B. Filtration

C. Distillation

D. Sedimentation

Answer: A

Q18. Painting is effective against rusting as long as:

A. The coating remains intact

B. The iron is kept wet

C. Salt is added

D. The paint is removed

Answer: A

Q19. Which is an example of corrosion prevention?

A. Galvanising an iron sheet

B. Leaving iron in rain

C. Adding salt to iron

D. Scratching an iron surface

Answer: A

Q20. Zinc protects iron partly because zinc is:

A. More reactive than iron

B. Less reactive than gold

C. A noble gas

D. A non-metal

Answer: A

Q21. Which method is commonly used for protecting iron gates?

A. Painting

B. Adding water

C. Adding salt

D. Removing all coating

Answer: A

Q22. Which method is commonly used to protect underground or moving machine components?

A. Oiling/greasing

B. Washing with salt

C. Exposing to moisture

D. Scratching

Answer: A

Q23. What happens if the zinc coating is damaged?

A. Zinc may still provide sacrificial protection to exposed iron under suitable conditions

B. Iron becomes a non-metal

C. Iron immediately melts

D. Oxygen disappears

Answer: A

Q24. Which method changes the composition of a metal to improve corrosion resistance?

A. Alloying

B. Painting

C. Oiling

D. Washing

Answer: A

Q25. Which of the following is a barrier method?

A. Painting

B. Scratching

C. Heating

D. Rusting

Answer: A

Q26. The main corrosive agents responsible for ordinary rusting are:

A. Oxygen and moisture

B. Nitrogen and helium

C. Hydrogen and nitrogen

D. Carbon and hydrogen

Answer: A

Q27. Why should damaged paint be repaired?

A. To prevent exposed metal from contacting air and moisture

B. To increase rusting

C. To increase salt content

D. To dissolve the metal

Answer: A

Q28. Which one is NOT a corrosion prevention technique?

A. Galvanisation

B. Painting

C. Oiling

D. Keeping iron in moist air

Answer: D

Q29. In galvanisation, the iron is coated with:

A. Zinc

B. Copper sulphate solution only

C. Sodium chloride

D. Water

Answer: A

Q30. The fundamental idea behind painting, oiling and galvanisation is to:

A. Reduce the contact of iron with corrosive surroundings

B. Increase moisture

C. Increase oxygen supply

D. Produce rust faster

Answer: A

10. 30 Subjective Questions with Answers / व्यक्तिपरक प्रश्न

1 Mark
Q1. How can corrosion be prevented?

Answer: Corrosion can be prevented by painting, oiling, greasing, galvanisation, electroplating and alloying.

1 Mark
Q2. What is galvanisation?

Answer: Galvanisation is the process of coating iron or steel with zinc to prevent corrosion.

1 Mark
Q3. Which metal is used for galvanising iron?

Answer: Zinc.

1 Mark
Q4. How does painting prevent rusting?

Answer: Paint forms a protective layer that prevents oxygen and moisture from reaching the iron surface.

1 Mark
Q5. Name one method other than painting used to prevent corrosion.

Answer: Galvanisation.

2 Marks
Q6. Why is iron painted?

Answer: Painting prevents direct contact of iron with oxygen and moisture, thereby reducing rusting.

2 Marks
Q7. What is the role of zinc in galvanisation?

Answer: Zinc forms a protective coating over iron and can provide sacrificial protection if the coating is damaged under suitable conditions.

2 Marks
Q8. Why does painting stop rusting?

Answer: Paint acts as a barrier and prevents oxygen and water from reaching the iron surface.

2 Marks
Q9. Name two methods of preventing corrosion.

Answer: Painting and galvanisation.

2 Marks
Q10. What happens when paint on an iron object gets scratched?

Answer: The exposed iron can come into contact with oxygen and moisture and may start rusting.

3 Marks
Q11. Explain galvanisation.

Answer:
Galvanisation is the process of coating iron or steel with a thin layer of zinc. The zinc coating prevents direct contact between iron and the environment and can also provide sacrificial protection when suitably exposed.

3 Marks
Q12. Explain how painting prevents rusting.

Answer:
1. Paint forms a protective coating.
2. It prevents oxygen from reaching iron.
3. It also prevents moisture from reaching iron.
4. Therefore, the conditions required for ordinary rusting are reduced.

3 Marks
Q13. Why is galvanisation more than just a barrier coating?

Answer: Zinc provides a physical barrier to the environment. Since zinc is more reactive than iron, it can also oxidise preferentially and provide sacrificial protection to exposed iron under suitable conditions.

3 Marks
Q14. Give three methods of preventing corrosion.

Answer:
1. Painting
2. Galvanisation
3. Oiling and greasing

3 Marks
Q15. Why should paint be reapplied on iron objects?

Answer: Paint may crack, peel or get scratched with time. Repainting restores the protective barrier and prevents oxygen and moisture from reaching the exposed iron.

4 Marks
Q16. Explain four methods of preventing corrosion.

Answer:
1. Painting: Provides a barrier against oxygen and moisture.
2. Oiling: Forms a protective film over the metal.
3. Galvanisation: Coats iron with zinc.
4. Electroplating: Deposits a protective metal coating using electricity.

4 Marks
Q17. Differentiate between painting and galvanisation.

Painting	Galvanisation
Paint is applied to the surface.	Zinc is coated on iron/steel.
Mainly acts as a barrier.	Acts as barrier and may provide sacrificial protection.
Scratches can expose iron.	Zinc can protect exposed iron under suitable conditions.

4 Marks
Q18. Why is zinc suitable for protecting iron?

Answer:
1. Zinc can form a protective coating over iron.
2. It prevents direct contact with air and moisture.
3. Zinc is more reactive than iron.
4. It can therefore provide sacrificial protection to exposed iron under suitable conditions.

4 Marks
Q19. Why does oiling prevent corrosion of machine parts?

Answer: Oil forms a continuous protective film on the metal surface. This reduces contact between the metal, oxygen and moisture, thereby reducing corrosion.

4 Marks
Q20. Why does a scratched painted iron surface rust?

Answer: Scratching removes the protective paint layer and exposes the iron. The exposed iron can then contact oxygen and moisture, allowing rusting to occur.

5 Marks
Q21. Explain the importance of galvanisation in preventing corrosion.

Answer:
Galvanisation protects iron by coating it with zinc. The zinc layer separates iron from air and moisture. Zinc is more reactive than iron and can undergo oxidation preferentially when exposed. Thus galvanisation provides both barrier protection and, under suitable conditions, sacrificial protection.

5 Marks
Q22. Explain why painting is an effective method for preventing rusting.

Answer:
Painting forms a protective layer over iron. This layer prevents oxygen and moisture from directly contacting the iron surface. Since both oxygen and moisture are required for ordinary rusting, painting greatly reduces rust formation. However, damaged paint must be repaired.

5 Marks
Q23. Explain the difference between barrier protection and sacrificial protection.

Answer:
Barrier protection: A coating prevents the metal from coming into contact with corrosive substances. Painting and oiling are examples. Sacrificial protection: A more reactive metal is used to protect the metal that needs protection. Zinc on iron in galvanisation can provide sacrificial protection under suitable conditions.

5 Marks
Q24. Why is corrosion prevention important?

Answer: Corrosion weakens metals, reduces their useful life and causes economic losses. Preventing corrosion improves safety, durability and reduces repair and replacement costs.

5 Marks
Q25. Explain five methods used to prevent corrosion.

Answer:
1. Painting
2. Oiling and greasing
3. Galvanisation
4. Electroplating
5. Alloying

These methods either isolate the metal from corrosive substances or improve its corrosion resistance.

6 Marks
Q26. Explain galvanisation of iron in detail.

Answer:
Galvanisation is the process of coating iron or steel with zinc. The zinc layer acts as a barrier between iron and oxygen/moisture. Zinc is also more reactive than iron, so if the coating is damaged, zinc can oxidise preferentially and provide sacrificial protection under suitable conditions. Therefore galvanisation provides effective protection against corrosion.

6 Marks
Q27. Explain how painting, oiling and galvanisation prevent corrosion.

Answer:
Painting: Forms a protective barrier between iron and air/moisture.

Oiling: Forms a water-repellent protective film over the metal.

Galvanisation: Covers iron with zinc. Zinc provides barrier protection and may also provide sacrificial protection when the coating is damaged.

6 Marks
Q28. A painted iron gate develops rust after the paint is damaged. Explain why.

Answer:
The paint normally prevents oxygen and moisture from reaching iron. When the paint is damaged, the underlying iron becomes exposed to air and moisture. The exposed iron undergoes electrochemical corrosion and forms rust. Therefore damaged paint should be repaired quickly to restore the protective barrier.

6 Marks
Q29. Compare different methods of corrosion prevention.

Method	Protection Mechanism
Painting	Barrier against air and moisture
Oiling/Greasing	Protective film
Galvanisation	Zinc coating + possible sacrificial protection
Electroplating	Protective metal coating
Alloying	Improves corrosion resistance through composition

6 Marks
Q30. "Galvanisation is better than painting for certain applications." Explain.

Answer:
Painting mainly provides barrier protection and depends on the paint layer remaining intact. Galvanisation coats iron with zinc. Zinc not only separates iron from the environment but can also provide sacrificial protection if the coating is damaged under suitable conditions. Therefore galvanisation can provide more durable protection in many applications such as iron sheets, pipes and steel products.

11. Quick Revision / त्वरित पुनरावृत्ति

Corrosion Prevention → Block Contact with Oxygen + Moisture

Painting → Protective Barrier

Oiling/Greasing → Protective Film

Galvanisation → Zinc Coating on Iron/Steel

Zinc → Barrier + Sacrificial Protection under suitable conditions

Damaged Paint → Exposed Iron → Rusting

⭐ CBSE Exam Booster:

Q. What is galvanisation?
Coating iron/steel with zinc to prevent corrosion.

Q. How does painting prevent rusting?
It prevents oxygen and moisture from reaching iron.

Q. Which metal is used in galvanisation?
Zinc.

Q. Why is zinc useful?
It provides a protective coating and can offer sacrificial protection to exposed iron under suitable conditions.