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NCERT Solutions for Class 8 Science Chapter 6 Combustion an...

NCERT Solutions for Class 8 Science Chapter 6 Combustion and Flame

Author at PW

January 21, 2026

Science becomes interesting when we observe things happening around us, like a candle burning or a gas stove working in the kitchen. In Class 8 Science Chapter 6, Combustion and Flame, students learn why some substances burn while others do not. The Combustion and Flame Class 8 questions and answers explain the process of burning, types of fuels, and safety measures in a simple manner. The explanations use daily-life examples, making the chapter easy to understand. Even students from Class 4 or Class 7 can easily grasp these concepts.

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Class 8 Science Chapter 6 Combustion and Flame Questions Answers

Here we have provided NCERT Solutions for Class 8 Science Chapter 6 for the ease of students so that they can prepare better for their exams.

1. List conditions under which combustion can take place.

Soln: The burning of a substance in the presence of oxygen is defined as combustion. The conditions under which combustion can take place are

The presence of air or oxygen.
The presence of fuel plays a significant role.
Ignition temperature is maintained (It is defined as the substance that catches fire at its lowest temperature.)

2. Fill in the blanks.

(a) Burning of wood and coal causes __________of air.

(b) A liquid fuel, used in homes is__________.

(d) The fire produced by oil cannot be controlled by___________ .

Soln:

(a) Burning of wood and coal causes pollution of air. (b) A liquid fuel, used in homes is kerosene . (c) Fuel must be heated to its ignition temperature before it starts burning. (d) The fire produced by oil cannot be controlled by water.

3. Explain how the use of CNG in automobiles has reduced pollution in our cities.

Soln:

Among cars, CNG contributes significantly to pollution reduction for the following reasons: In comparison, CNG is a cleaner fuel. As an alternative to petrol, diesel, and propane/LPG, consider using CNG. Compared to the other fuels indicated above, it typically contains a few more unwanted gases. When fuels like petroleum burn, a lot of unburned carbon particles are released into the air along with carbon monoxide, which can cause respiratory illnesses.

4. Compare LPG and wood as fuels.

Soln:

Wood

It is regarded as a conventional fuel that can be utilized for both household and commercial uses. A large amount of smoke from wood pollutes the air and leads to respiratory illnesses. Deforestation is largely caused by the consumption of timber. Wood has a calorific value of between 17,000 and 22,000 kJ/kg. On the other hand, wood can be used for a campfire or furnace outside as well as an indoor furnace, stove, or fireplace.

LPG

The application of Wood has been substituted by Liquefied Petroleum Gas (LPG). It doesn't emit any toxins or smoke. The fuel is cleaner. LPG has a higher fuel efficiency than wood. LPG has a calorific value of 55,000 kJ/kg. LPG is therefore the best option.

5. Give reasons.

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

(b) LPG is a better domestic fuel than wood.

Soln:

a) Water is an excellent electrical conductor.

Water wouldn't do anything but spread the electricity in an electrical fire. Someone putting out the flames could receive an electric shock.

b) Unlike wood, which releases smoke and other pollutants, LPG is a cleaner fuel.

Conversely, wood produces a great deal of smoke and pollutants into the atmosphere, which contaminates it and causes respiratory illnesses. For this reason, LPG is a superior home fuel than wood.

c) Due to its low ignition temperature, the paper itself easily catches fire.

Because aluminum is an excellent electrical conductor, the sheet of paper wrapped around the pipe doesn't catch fire. However, the temperature at which paper is wrapped around an aluminum pipe rises. Therefore, heat is transferred from the paper to the aluminum pipe. It doesn't catch fire as a result.

6. Make a labeled diagram of a candle flame.

Soln:

Labelled diagram of Candle Flame

7. Name the unit in which the calorific value of a fuel is expressed.

Soln:

Calorific value is defined as the energy contained in the fuel. It is expressed in the form kJ/kg kJ=kilo joules and kg=kilogram

8. Explain how CO ₂can control fires.

Soln:

As a non-flammable gas, CO2 puts out the fire in two ways: (i) Because it weighs more than oxygen, it blankets the flames and prevents oxygen from coming into touch with fuel. (ii) CO2 is stored in liquid form in cylinders. When it is released, it greatly expands. This lowers the fuel's temperature, aiding in the containment of the fire.

9. It is difficult to burn a heap of green leaves but dry leaves catch fire easily. Explain.

Soln:

The high igniting temperature of a pile of green leaves is caused by their high moisture content. It does not readily catch fire as a result. However, dried leaves have a low ignition temperature because they are devoid of moisture. As a result, they burn easily.

10. Which zone of a flame does a goldsmith use for melting gold and silver and why?

Soln:

The non-luminous flame, which is thought to be the outermost portion of the flame, is mostly used by goldsmiths. Because the outermost flame completely burns and is thought to be the hottest component of the flame, this portion of the flame is used.

11. In an experiment, 4.5 kg of fuel was completely burnt. The heat produced was measured to be 180,000 kJ. Calculate the calorific value of the fuel.

Soln:

NCERT Solutions for Class 8 Science-chpater-6-sol-1

12. Can the process of rusting be called combustion? Discuss.

Soln:

No, because heat is released during the rusting process, rusting is an exothermic reaction. In contrast, combustion is a chemical reaction that releases energy in the form of light or heat when a material combines with oxygen.

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?

Soln:

Given that it is the hottest area of the flame and is considered non-luminous, water placed in its outermost part will heat up quickly. Thus, we shall heat Ramesh's beaker first. On the other hand, Abida, who positioned the beaker in the yellow flame, is relatively less heated.

What is Combustion?

Combustion is just a fancy word for burning. When a substance reacts with oxygen to emit heat, we call it combustion. The things that can burn are called "combustible" substances, or simply fuels. Fuels can be solid like wood, liquid like petrol, or gas like the LPG we use for cooking.

When you study combustion and flame class 8 questions and answers ncert, you'll learn that for a fire to start, we need three things:

Fuel: Something to burn.
Air: Specifically, oxygen in air.
Heat: To reach a certain temperature so the fire can start.

If you take away any of these three, the fire will go out. This is a very important part of staying safe!

The Ignition Temperature

Have you ever wondered why a piece of paper catches fire quickly, but a big log of wood takes a long time? This is because of the "Ignition Temperature." This is the lowest temperature at which a substance catches fire.

Paper has a low ignition temperature, so it burns fast. Wood has a higher one, so we need to heat it up more before it starts to burn. In combustion and flame class 8 questions and answers extra, we often see questions about why we use "fire starters" like kerosene or small twigs to get a big fire going. It's about reaching that special temperature!

Different Types of Combustion

Fire doesn't always look or act the same way. There are three main ways things burn:

Rapid Combustion: This happens when you turn on a gas stove. The gas burns quickly and produces heat and light immediately.
Spontaneous Combustion: This is a bit scary! It happens when something bursts into flame suddenly without any apparent cause. For example, some coal dust in mines can catch fire all by itself.
Explosion: When you light a firecracker, it burns very, very fast. It makes a loud sound and gives off a lot of heat, light, and gas. This is called an explosion.

Learning these types is a big part of combustion and flame class 8 questions and answers cbse preparation.

Check Out: Class 8 Combo Set of 5 Books

How Do We Control Fire?

Fire is a good servant but a bad master. If a fire gets too big, we need to stop it. As we talked about earlier, we do this by removing one of the three requirements for fire.

Using Water: Water cools the material so it goes below its ignition temperature. It also creates a vapor blanket that cuts the air. However, we don't use water for electrical fires or oil fires because it can be dangerous!
Carbon Dioxide (CO_2): For fires involving electricity or oil, CO_2 is the best fire extinguisher. It is heavier than oxygen, so it covers the fire like a blanket and cuts off the air supply.

Combustion and flame class 8 questions and answers ncert: Chapter Solutions

Q1: List the conditions under which combustion can take place.

For combustion to happen, we need three things: a combustible substance (fuel), a steady supply of oxygen (air), and enough heat to reach the ignition temperature.

Q2: Fill in the blanks.

Burning of wood and coal causes pollution of air.
A liquid fuel used in homes is LPG.
Fuel must be heated to its ignition temperature before it starts burning.
Fire produced by oil cannot be controlled by water.

Q3: Explain how CNG use in automobiles has reduced pollution in our cities.

CNG stands for Compressed Natural Gas. It is a much cleaner fuel than petrol or diesel. When it burns, it produces very small amounts of harmful gases and leaves no ash behind. This keeps our air cleaner.

Q4: Compare LPG and wood as fuel.

LPG is better than wood because it doesn't produce smoke, it has a higher calorific value (it gives more heat), and it doesn't leave any ash behind. Wood produces smoke that is bad for our lungs and it leaves a lot of mess.

Q5: Why is paper wrapped around an aluminum pipe hard to burn?

Aluminum pipe is a good conductor of heat. When we try to burn the paper, the heat quickly passes into the metal pipe. Because the heat is taken away, the paper doesn't reach its ignition temperature easily and doesn't burn.

Understanding the Flame

When you look at a candle, you see a flame. But did you know the flame has different parts? Not all parts of the flame are equally hot!

The Three Zones of a Flame:

The Outer Zone: This is the blue part. It is the hottest part of the flame because it gets plenty of oxygen. This is where "complete combustion" happens.
The Middle Zone: This part is yellow. It is moderately hot. Here, "incomplete combustion" happens, creating tiny glowing carbon particles. This is why it looks bright.
The Inner Zone: This is the black part near the wick. It is the coolest part because it contains unburnt vapors of the wax.

Goldsmiths use the outermost (blue) part of the flame with a metallic blow-pipe to melt gold and silver because it is the hottest spot!

What Makes a Good Fuel?

In your combustion and flame class 8 questions and answers pdf, you will find that a "perfect" fuel doesn't really exist, but we look for a "good" fuel. A good fuel should:

Be cheap and easy to find.
Burn easily in air at a moderate rate.
Produce a large amount of heat.
Do not leave unwanted or harmful substances.

The amount of heat produced when 1 kg of fuel is completely burnt is called its Calorific Value. It is measured in a unit called kilojoules per kilogram (kJ/kg).

Harmful Effects of Burning Fuels

Even though fuels help us cook and travel, burning them can hurt the environment.

Carbon Dioxide (CO_2): Burning most fuels releases CO_2. Too much of this in the air leads to "Global Warming," which makes the Earth too hot.
Carbon Monoxide (CO): If a fuel doesn't burn completely in a closed room, it makes CO. This gas is very poisonous and can even kill people sleeping in that room.
Acid Rain: Burning coal and diesel releases oxides of sulfur and nitrogen. These mix with rain to make acid rain, which damages buildings, plants, and soil..

Combustion and Flame class 8 Questions and Answers Extra - For Clever Students

Q1: Why do we wrap a person whose clothes are on fire in a blanket?

Wrapping a person in a thick blanket stops the air (oxygen) from reaching the fire. Without oxygen, the fire cannot burn and it goes out immediately.

Q2: What is "spontaneous combustion"?

It is a type of combustion where a material suddenly bursts into flames without being heated by a matchstick or a lighter. It usually happens in coal mines or with phosphorus in summer.

Q3: Can we use a matchstick to light a log of wood directly?

No, because a matchstick doesn't produce enough heat to raise the temperature of a big log of wood to its ignition temperature. We need to use paper or kerosene as a middle step.

Check Out: PW School Books

Benefits of PW Class 8 Study Material

Simple and Clear Explanations
PW Class 8 study material explains every topic in easy language, helping students understand concepts without confusion.

Strictly NCERT-Based
The content follows the latest NCERT syllabus, making it reliable for school exams and revisions.

Well-Organised Notes
Chapter-wise notes with examples and diagrams make learning smooth and effective.

Ample Practice Questions
Practice exercises with detailed solutions help improve accuracy and confidence.

Builds Strong Basics
Regular study using PW material strengthens fundamentals for higher classes and competitive exams.

Class 8 Science Chapter 6 Combustion and Flame FAQs

1. Where can I find the combustion and flame class 8 questions and answers pdf?

You can find it on the PW Store website.

2. Why is the flame of a candle yellow?

The middle part of the flame is yellow from incomplete combustion. The tiny bits of carbon become hot and glow yellow, giving the flame its color.

3. What is the best way to put out an electrical fire?

Never use water! Use a CO_2 fire extinguisher or throw sand on the fire. This stops the air without giving you an electric shock.

4. What is the hottest part of a flame?

The outermost blue zone is the hottest part because it gets the most oxygen from the surrounding air.

At the end of the day, understanding fire helps us use it safely. We hope these combustion and flame class 8 questions and answers make your science class feel like a breeze! Always remember to be careful around fire and never play with matches.

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