NCERT Solutions For Class 8 Science Chapter 4 Combustion and Flame - 2025-26

1. List Conditions Under Which Combustion Can Take Place.

Ans: Combustion takes place under the following three conditions: 

(i) In the presence of fuel.

(ii) In the presence of oxygen (air).

(iii) In the presence of heat - the minimum temperature at which a substance catches fire, known as ignition temperature.

2. Fill in the Blanks:

a) Burning of wood and coal causes ______ of air.

Ans: Burning of wood and coal causes pollution of air.

b) A liquid fuel used in homes is _____.

Ans: A liquid fuel used in homes is Liquified Petroleum Gas (LPG).

c) Fuel must be heated to its ____ before it starts burning.

Ans: Fuel must be heated to its ignition temperature before it starts burning.

d) The fire produced by oil cannot be controlled by _____.

Ans: Fire produced by oil cannot be controlled by water.

3. Explain How the Use of CNG in Automobiles Has Reduced Pollution in Our Cities.

Ans: The use of CNG in automobiles has reduced pollution in our cities because it is a clean fuel and the amount of unburnt fuel in CNG is very less compared to petroleum. It does not produce smoke and harmful substances that are produced in petroleum.

4. Compare LPG and Wood as Fuels.

Ans: The difference between LPG and wood as fuels is: 

5. Give Reasons.

a) Water is not used to control fires involving electrical equipment.

Ans: Water is not used to control fires involving electrical equipment because water is a good conductor of electricity due to which the person may be electro-conducted and it may damage the equipment.

b) LPG is a better domestic fuel than wood.

Ans: LPG is a better domestic fuel than wood because wood produces a lot of smoke on combustion and causes respiratory problems. Also, its efficiency is lower than LPG.

c) Paper by itself catches fire easily whereas a piece of paper wrapped around an aluminum pipe does not.

Ans: Paper by itself catches fire easily whereas a piece of paper wrapped around an aluminum pipe does not because aluminum is a good conductor of heat which absorbs the heat from the paper and the paper does not catch fire. Whereas, the paper by itself catches fire.

6. Make a Labeled Diagram of a Candle Flame.

Ans: A labeled diagram of a candle flame is: 

7. Name the Unit in Which the Calorific Value of a Fuel is Expressed.

Ans: “Kilo Joule per Kilogram $\left( kJ/kg \right)$” is used to express the calorific value of a fuel.

8. Explain how \[\mathbf{C}{{\mathbf{O}}_{\mathbf{2}}}\] is able to control fires.

Ans: We know that combustion takes place under the following three conditions: 

(i) In the presence of oxygen (air).

(ii) In the presence of fuel.

(iii) In the presence of heat - the minimum temperature at which a substance catches fire, known as ignition temperature.

We can control the fire if any one of the three conditions is not met. 

(i) $C{{O}_{2}}$ is heavier than oxygen and hence it acts as a protective blanket and prevents oxygen from reaching the fire.

(ii) Since $C{{O}_{2}}$ is stored in a liquid state, therefore, when it is used on the fire, it expands and cools which lowers down the temperature. This prevents heat from reaching the fire.

9. It is Difficult To Burn a Heap of Green Leaves, but Dry Leaves Catch Fire Easily. Explain.

Ans: It is difficult to burn a heap of green leaves, but dry leaves catch fire easily because combustion takes place in the presence of heat - the minimum temperature at which a substance catches fire, known as ignition temperature. Green leaves have high moisture than dry leaves and hence, it takes more time for green leaves to reach ignition temperature than dry leaves.

10. Which Zone of a Flame Does a Goldsmith Use for Melting Gold and Silver and Why?

Ans: Goldsmiths use the outermost zone of the flame to melt gold and silver because gold and silver have a high melting point and the outermost part undergoes complete combustion and it is the hottest part of the flame which supply the adequate amount of heat required for melting. 

11. In an Experiment \[\mathbf{4}.\mathbf{5}\text{ }\mathbf{kg}\] of a fuel was completely burnt. The heat produced was measured to be \[\mathbf{180},\mathbf{000}\text{ }\mathbf{kJ}\]. Calculate the calorific value of the fuel.

Ans: The amount of heat released during combustion of $1\text{ }kg$ fuel is known as calorific value i.e., 

$Calorific\text{ }Value=\dfrac{Heat\text{ produced during combustion}}{Quantity\text{ of fuel}}$  

$\Rightarrow Calorific\text{ }Value=\dfrac{180,000}{4.5}\text{ }kJ/kg$

$\therefore Calorific\text{ }Value=40,000\text{ }kJ/kg$

12. Can the Process of Rusting Be Called Combustion? Discuss.

Ans: A chemical process in which a substance reacts with oxygen to give off heat is called combustion. When an iron metal combines with the oxygen in the presence of water to form a compound iron oxide is known as rusting. 

Therefore, the process of rusting can be called combustion because in both processes, heat, and light are produced. Rusting is known as slow combustion. 

13. Abida and Ramesh Were Doing an Experiment in Which Water Was To Be Heated in a Beaker. Abida Kept the Beaker Near the Wick in the Yellow Part of the Candle Flame. Ramesh Kept the Beaker in the Outermost Part of the Flame. Whose Water Will Get Heated in a Shorter Time?

Ans: A labeled diagram of a candle flame is:

Observe that the innermost zone of the candle which is near to the wick is the least hot whereas the outer zone of the candle is the hottest part of the candle flame.

Since Ramesh kept the beaker in the outermost part of the flame, therefore his beaker will be heated in a shorter time as compared to Abida.

Class 8 Science Chapter 4 Quick Overview of Topics - Combustion and Flame

Combustion and Flame Class 8 Science Chapter 4 NCERT Solutions - Quick Overview of Detailed Structure of Topics and Subtopics Covered.

Combustion and Flame; Class 8 NCERT Solutions Chapter 4  Important Topics

1. Types of Combustion:

• Rapid Combustion: Occurs quickly with the production of heat and light, such as a burning matchstick.

• Spontaneous Combustion: Occurs without external heat, like the ignition of hay in a barn.

• Explosive Combustion: A sudden reaction with the release of gases and heat, such as fireworks.

2. Structure of a Flame:

• Inner Zone: The least hot part of the flame, which is dark and surrounds the wick.

• Middle Zone: Moderately hot, where partial combustion occurs, often appears yellow.

• Outer Zone: The hottest part of the flame, blue in color, where complete combustion occurs.

3. Ignition Temperature:

• Definition: The minimum temperature at which a substance catches fire.

• Significance: Different substances have different ignition temperatures, affecting their ease of ignition.

4. Inflammable Substances:

• Definition: Substances that catch fire easily.

• Examples: Petrol, alcohol, LPG.

5. Control of Fire:

• Methods: Removing one of the three elements necessary for combustion (fuel, heat, oxygen).

• Fire Extinguishers: Different types, including water, foam, and carbon dioxide extinguishers.

Benefits of  Vedantu’s NCERT Solutions for Chapter 4 Science Class 8 Combustion and Flame

Referring to Vedantu’s NCERT Class 8 Science Solutions has several benefits. Some of them are:

• Detailed explanations and step-by-step solutions for all topics in Chapter 4.

• Solutions curated by experienced educators to ensure accuracy and clarity.

• Learn about the structure of a flame, including the various zones and their characteristics, and the reasons behind the different colours observed in flames.

• The understanding related to topics like delving into the properties of different fuels, their calorific values, and how to determine the efficiency of a fuel.

• Clear and concise explanations using precise chemical terminology.

• In-depth analysis of key concepts and their applications in real-life scenarios.

• Combustion and Flame class 8 questions and answers pdf explains the types of Combustion and Structure of Flames..

• Solutions to a variety of problems to strengthen analytical and problem-solving abilities.

• Step-by-step solutions for numerical problems and reaction mechanisms.

Conclusion 

The class 8 science chapter Combustion and Flame serves as an invaluable resource for young learners to understand the fundamental principles of combustion and the science of flames. Combustion and Flame Class 8 PDF sheds light on the chemical processes underlying combustion, the various types of flames, and their significance in daily life. The provided solutions offer clear explanations and elucidate the scientific phenomena behind these processes. By mastering these concepts, students not only gain scientific knowledge but also develop a heightened awareness of fire safety and environmental concerns. These NCERT solutions, with their comprehensive approach, empower students to grasp the intricate science of combustion, making them a vital aid for academic excellence and informed citizenship.

Important Study Materials for Class 8 Chemistry Chapter 4 Combustion and Flame

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NCERT Solutions for Class 8 Science-Chapter wise PDF Links

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