NCERT Solutions Class 8 Science Chapter 6

NCERT Solutions for Class 8 Science Chapter 6

Science is one of the most ancient and influential academic fields, covering various topics. Science helps us comprehend the world around us. Everything we know about the cosmos is the result of scientific investigation and experiment, from how trees reproduce to what an atom comprises. 

NCERT Class 8 Science Chapter 6 is Combustion and Flame. The subtopics of combustion, types of combustions, the function of oxygen in combustion, ignition temperature, flammable substances, fire management, definition and distinct zones of flame, toxic pollutants, acid rain, and its consequences are covered in this chapter.

The subject experts have prepared Class 8 Science Chapter 6 Solution at Extramarks. Going through the NCERT Solutions of this chapter is essential for students to get better results in the examination. Hence, Extramarks provides NCERT Solutions of Combustion and Flame Class 8. These solutions not only help to learn the concepts but also to retain them easily and quickly.

Extramarks can be a one-stop solution for all students’ problems. Apart from NCERT Solution of Class 8 Science Chapter 6- Combustion and Flame, NCERT Solutions, Additional Questions, Sample Papers, Revision Notes, CBSE Past  years’ question papers, and a lot more can be found on the Extramarks website. 

Key Topics Covered in NCERT Solutions for Class 8 Science Chapter 6

Extramarks makes study easier for the students by identifying  the key topics that are covered in NCERT Solutions for Class 8 Science Chapter 6 are given below: 

What is combustion? 
How do we control fire?
Types of combustion
Structure of a flame
What is a fuel?
Fuel efficiency
Burning of fuel leads to harmful products

Let us look at the in-depth information provided by Extramarks on each subtopic in NCERT Solutions for Class 8 Science Chapter 6.

What is combustion? 

Combustion is the process of a material undergoing a chemical reaction in the presence of air (oxygen) to create heat and light.

Combustible materials are those that may burn easily. However, in the absence of oxygen, combustion is impossible.

Combustible and Non-Combustible Substances

Extramarks NCERT Solutions for Class 8 Science Chapter 6 describes combustible and non-combustible substances as follows:

Combustible Substances: Materials such as wood, coal, and paper that catch flame quickly are called combustible substances.

Non-Combustible Substances: Materials such as sand, glass, and water that do not catch flame easily are known as non-combustible substances

How do we control fire?

By eliminating one or more conditions that are necessary for the production of fire, fire can be regulated.

Because it can make the situation worse, water is frequently used to put out fires started by things other than electrical equipment and oil.

Oil or electrical equipment fires cannot be put out with water; instead, a fire extinguisher or sand is employed to do it.

Fire Control

Any or all the elements of combustion, such as fuel, oxygen (air), and ignition temperature, can be removed to regulate fire (by lowering the temperature).

Fire Extinguisher

  • A fire extinguisher is a gadget that the fire department uses to put out fires.
  • Extinguishers work by cutting off the supply of oxygen or lowering the temperature of the fuel, or both.

Types of Combustions

The kind of combustion is determined by the fuel utilised. NCERT Solutions for Class 8 Science Chapter 6 states that combustions are categorised into three groups based on their nature and severity. They are:

  • Rapid combustion: Rapid combustion occurs when a material burns quickly and generates both heat and light—for instance, a matchstick burning on a gas stove.
  • Spontaneous combustion is the form of combustion in which a substance spontaneously bursts into flames without any apparent reason, known as spontaneous combustion. For example, phosphorus and camphor combustion.
  • Explosion: A considerable volume of gas is released during the reaction. An explosion is a name for such a response—a firework or missiles.


NCERT Solutions for Class 8 Science Chapter 6 explains flame as the visible and gaseous element of fire. The light energy emitted by fuel burning is what we perceive as flame.

Structure of a flame

  • The hottest zone of all is the outermost zone, which is blue due to total combustion. It’s the section of the flame that doesn’t glow.
  • Partially burning fuel occurs in the centre zone of the candle flame, which is pretty hot and yellow. It’s the flame’s brightest component.
  • The least hot part of the flame is the innermost zone, black. This is because there are unburned wax vapours present.

Zones of a Candle

There are three zones of a candle:

  • Outer zone- The zone of complete combustion is the hottest part of the flame.
  • The zone of partial combustion is referred to as the middle zone and it is moderately hot.
  • The innermost zone of a candle is the zone of unburnt wax vapours, and it is the coolest part of the flame.

What is a fuel?

  • Fuel is any material that, when burned, provides a usable amount of energy—for instance, fossil fuels, biogas, nuclear power, and so on.
  • Depending on its condition, a fuel might be solid, liquid, or gas.
  • It might be natural or manufactured, depending on the circumstances.

Fuel efficiency

Extramarks NCERT Solutions for Class 8 Science Chapter 6 briefs you about calorific value and efficiency of fuels:

  • The heat energy produced when 1 kilogramme of fuel is completely burned is referred to as the calorific value of the fuel. Therefore, the calorific value of a fuel is measured in kilojoules per kilogramme (kJ/kg).
  • The proportion of energy released by a fuel combustion process turned into meaningful work is called efficiency.
  • The efficiency of a product is related to its calorific value. When the value is high, the efficiency also is high. However, if the value is low, the efficiency will be poor as well.

Ideal Fuel

  • The ideal fuel is inexpensive, readily available, and flammable.
  • It has a lot of calorific value.
  • It does not harm the environment with toxic gases or residues.

Burning of fuel leads to harmful products

Some harmful effects of burning fuels as per Extramarks NCERT Solutions for Class 8 Science Chapter 6 are:

  • Unburned carbon particles are released by carbon-containing fuels such as wood, coal, or any fossil fuel (called suits). These are hazardous chemicals that cause respiratory illnesses, including asthma and cancer.
  • Carbon monoxide is a harmful gas produced due to the incomplete combustion of carbon fuels, and prolonged exposure can be lethal.
  • Global warming is caused by an increase in the concentration of carbon dioxide in the air, often known as a greenhouse gas.
  • Sulphur and nitrogen oxides dissolve in rainfall, forming acids. Acid rain is the name given to such a downpour. It is highly hazardous to crops, structures, and soil because it raises soil acidity and accelerates metal corrosion.

Extramarks NCERT Solutions for Class 8 Science Chapter 6 explains different aspects of pollution and its effects on the environment. To get more information on the subject, refer to the Extramarks website.

CNG (Compressed Natural Gas) is used as a replacement for diesel and petrol as automotive fuels since it is less polluting and cleaner. Because compressed natural gas (CNG) occurs naturally, it is a clean fuel. In addition, it is ecologically beneficial since it includes minimal nitrogen dioxide, carbon dioxide, and sulphur dioxide levels. As a result, incidences of respiratory difficulties and asthma episodes are reduced.

CNG cars have a 10–12-year lifetime and are inexpensive and ecologically beneficial. In addition, this results in cheaper machine maintenance costs.

CNG is environmentally friendly since its primary component is methane, a waste gas. Because of the way it’s kept, it’s also safer and less combustible than carbon fuels. In addition, the CNG cylinders are made of a durable carbon fibre reinforced material.

It includes a low amount of nitrogen oxide, which contaminates engine oil. CNG is a cleaner fuel. So, the oil produces fewer damages, and the automobile will require less maintenance.

NCERT Solutions for Class 8 Science Chapter 6- NCERT Solutions Article Links

Preparing through the NCERT Solutions of any chapter is the best way to grasp all the topic-wise concepts of the entire chapter. Subject experts prepare these solutions to meet all the requirements of the students. Click on the  links below to view NCERT Solutions for Class 8 Science Chapter 6:

Class 8 Science Chapter 6: Very Short Answer Type Questions

Class 8 Science Chapter 6: Short Answer Type Questions

Class 8 Science Chapter 6: Long Answer Type Questions

Students may access NCERT Solutions for Class 8 Science Chapter 6 and other chapters by clicking here. In addition, students can also explore NCERT Solutions for other classes from the links below.

  • NCERT Solutions Class 1
  • NCERT Solutions Class 2
  • NCERT Solutions Class 3
  • NCERT Solutions Class 4
  • NCERT Solutions Class 5
  • NCERT Solutions Class 6
  • NCERT Solutions Class 7
  • NCERT Solutions Class 8
  • NCERT Solutions Class 9
  • NCERT Solutions Class 10
  • NCERT Solutions Class 11
  • NCERT Solutions Class 12

By getting access to NCERT Solutions for Class 8 Science Chapter 6– Combustion and Flame, students can easily understand all the concepts of the chapter.

Key Features of NCERT Solutions for Class 8 Science Chapter 6

Extramarks’ NCERT Solutions are composed of meticulously designed and prepared concise answers of each chapter, considering the students’ requirements. These solutions benefit students greatly and assist them in comprehending the concepts more easily and quickly. Why should a student invest his  valuable time with us? We’ll explain why:

  • Practising these NCERT Solutions helps students in memorising the concepts and preparing  them with the writing framework for the examination.
  • These solutions have been made in simple language to make it convenient for the students to grasp the concepts.
  • These solutions are prepared keeping the NCERT guidelines in mind.

Q.1 List conditions under which combustion can take place.

Ans. Necessary conditions for combustion are:

  1. Fuel: Fuel is the raw material for combustion.
  2. Air: Combustion takes place only in the presence of air or oxygen.
  3. Heat: Heat is required to raise the temperature of a fuel so that it attains its ignition temperature. Ignition temperature is the minimum temperature at which a substance catches fire and starts burning.

Q.2 Fill in the blanks.

  1. Burning of wood and coal causes ___________ of air.
  2. A liquid fuel, used in homes is _______.
  3. Fuel must be heated to its __________ __________ before it starts burning.
  4. Fire produced by oil cannot be controlled by ______________.


1. pollution
2. LPG
3. ignition temperature
4. water

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

Ans. Combustion of fuels like petrol and diesel produces un-burnt particles along with carbon monoxide gas. These pollutants cause many respiratory problems. Oxides of sulphur and nitrogen are also released due to combustion of petrol and diesel. Oxides of sulphur and nitrogen cause acid rain. CNG produces less harmful products and does not cause much of air pollution. It is therefore, called as cleaner fuel.

Q.4 Compare LPG and wood as fuels.


Comparison of LPG and wood as fuels

LPG as fuel Wood as Fuel
Burning of LPG does not produce smoke and other pollutants. It is a cleaner fuel. Burning of wood produces a lot of smoke and other pollutants which may cause respiratory problems.
LPG is a liquefied form of petroleum. Wood is obtained from trees. Therefore, use of wood as fuels may lead to deforestation.
Calorific value of LPG is very high (55000 kJ/kg). Calorific value of wood is low (17000 -22000 kJ/kg).

Q.5 Give reasons.

  1. Water is not used to control fires involving electrical equipment.
  2. LPG is a better domestic fuel than wood.
  3. Paper by itself catches fire easily whereas a piece of paper wrapped around an aluminium pipe does not.


  1. Water cannot be used to put off fire caused by the electrical equipments because it may conduct electricity and harm those trying to douse the fire.
  2. Burning of wood produces a lot of smoke and un-burnt particles cause respiratory problems. LPG does not produce smoke and its calorific value is much higher as compared to wood. Therefore, LPG is a better domestic fuel than wood.
  3. For burning, a combustible substance must attain its ignition temperature. Piece of paper wrapped around an aluminium pipe does not catch fire on heating because it is unable to reach its ignition temperature due to transfer of heat to aluminium pipe which is a good conductor of heat.

Q.6 Make a labelled diagram of a candle flame.


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

Ans. Calorific value of a fuel is expressed in Kilo Joule per kg (kJ/kg).

Q.8 Explain how CO2 is able to control fires.


  • Carbon dioxide is the best extinguisher for fires involving electrical equipments and inflammable materials like petrol because CO2 is heavier than oxygen and it covers the fire like a blanket.
  • It controls fire by cutting off the supply of oxygen.

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

Ans. A heap of leaves contains a lot of water. Due to presence of water, ignition temperature of green leaves is not reached easily. Hence, it is difficult to burn a heap of green leaves. Dry leaves do not contain water. Therefore, ignition temperatures of dry leaves are easily attained and catch fire easily.

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

Ans. Goldsmith uses outermost zone of the flame for melting gold and silver. This is because the outermost zone of the flame is hottest part of the flame. In this zone complete combustion takes place.

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

Ans. Calorific value of the fuel is the amount of heat energy produced on complete combustion of 1 kg of fuel.

Amount of heat produced by 4.5 kg of fuel = 180,000 kJ

Therefore, heat produced by 1 kg of fuel = 180,000/4.5

= 40,000 kJ/kg

Hence, calorific value of given fuel is 40,000 kJ/kg.

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

Ans. Combustion is the chemical process in which a substance reacts with oxygen and gives out energy in the form of either heat or light or both. It is a very fast process. On the other hand, rusting is a slow process which involves the conversion of iron into rust in presence of air (oxygen) and water. In both the processes, oxygen is common reactant.

Q.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. The water in the Ramesh’s beaker will require shorter time for heating. This is because Ramesh kept beaker in the outermost part of the flame which is hottest zone of the candle flame. The water in Abida’s beaker will take comparatively longer to heat up as the yellow zone is less hot when compared to the outermost part of the flame.

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FAQs (Frequently Asked Questions)
1. According to chapter 6 of Science Class 8, how many questions are there for practice in the NCERT?

The NCERT Solution for Class 8 Science Chapter 6 Combustion and Flames has 13 questions and answers. This chapter includes fill-in-the-blanks, reasoning, short answer questions, drawing, and numerical-value type problems. Every question in this exercise helps students check their grasp of the ideas, and the Extramarks website has well-explained answers to all these questions.

2. How can one differentiate between flame and combustion?

The most fundamental distinction between flame and combustion is that combustion refers to simply heating without flames since most of the energy in combustion is transferred to heat, resulting in less light energy than flame. Conversely, flames are created when any article burns during the combustion process.