NCERT Solutions Class 8 Science Chapter 4 Combustion and Flame

Combustion and Flame, the fourth chapter of Class 8 Science, delves into essential concepts related to fire and its control. In Class 8 Science Chapter 4, students will explore topics such as What is Combustion?, the process behind burning, and How Do We Control Fire?, providing practical knowledge on fire safety. The chapter further explains the Types of Combustion, shedding light on different combustion reactions, and the Structure of a Flame, breaking down its various zones. Additionally, students will learn about What is a Fuel? and the significance of Fuel Efficiency, which is important for understanding how fuels are used effectively and sustainably. This chapter is key in building a strong foundation for understanding energy sources and fire safety practices.

1.0Download NCERT Solutions for Class 8 Science Chapter 4 PDF

This article provides Class 8 Combustion and Flame solutions aligned with NCERT guidelines. By practicing these solutions, students can build a solid foundation in chemistry and improve their problem-solving skills, ultimately helping them achieve better scores in board exams. For a deeper understanding, students can download the Class 8 Science Chapter 4 Combustion and Flame exercise solutions below, curated by ALLEN’s experts.

2.0Class 8 Science Chapter 4 Combustion and Flame - Overview

Before getting into the details of class 8 combustion and flame NCERT solutions, let's take a brief look at the topics and subtopics covered in this chapter of the NCERT Class 8 Science book.

Class 8 Science Topics

What is Combustion? – Explores the process of burning and how chemical energy is converted into heat and light.

How Do We Control Fire? – Teaches methods to safely manage and extinguish fires to prevent damage and harm.

Types of Combustion – Covers different combustion processes like complete, incomplete, and spontaneous combustion.

Flame – Introduces the nature of flames and how they represent the visible part of a combustion reaction.

Structure of a Flame – Explains the different zones of a flame, each indicating varying temperatures and reactions.

What is a Fuel? – Defines what constitutes a fuel and how fuels are used to generate energy.

Fuel Efficiency – Discusses how to maximize energy output from fuels while minimizing waste and environmental impact.

3.0NCERT Questions with Solutions Class 8 Science Chapter 4 - Detailed Solutions

• List conditions under which combustion can take place. Ans. There are three essential conditions of combustion: (a) Presence of a combustible substance. (b) Presence of oxygen i.e., supporter of combustion. (c) Attainment of ignition temperature.
• Fill in the blanks (a) Burning of wood and coal causes of air. (b) A liquid fuel, used in homes is _. (c) Fuel must be heated to its before it starts burning. (d) Fire produced by oil cannot be controlled by _. Ans. (a) Pollution (b) LPG (c) Ignition temperature (d) Water.
• Explain how the use of CNG in automobiles has reduced pollution in our cities. Ans. CNG is cheap, readily available and highly combustible. It has high calorific value. It does not produce gases or residues when used in automobiles, so it reduced the pollution in our cities. The use of CNG in automobiles has reduced pollution in our cities because CNG produces the harmful product in very small amount and it is a cleaner fuel.
• Compare LPG and wood as fuels. Ans.

• Give reasons : (a) Water is not used to control fires involving electrical equipment. (b) LPG is a better domestic fuel than wood. (c) Paper by itself catches fire easily whereas a piece of paper wrapped around an aluminium pipe does not. Ans. (a) Water is not used to control the fire involving electric equipment because it is a good conductor of electricity and harm those trying to douse the fire. (b) LPG is better domestic fuel than wood because it neither produce gases nor residues that pollute the environment. (c) The paper by itself catches fire easily because its ignition temperature is low, while a piece of paper wrapped around an aluminium pipe does not catches fire, because its ignition temperature rises.
• Make a labelled diagram of a candle flame. Ans.

• Name the unit in which the calorific value of a fuel is expressed. Ans. The calorific value of a fuel is expressed in a unit called kilojoule per $\mathrm{kg}(\mathrm{kJ}/\mathrm{kg})$.
• Explain how ${\mathrm{CO}}_2$ is able to control fires. Ans. ${\mathrm{CO}}_2$, being heavier than oxygen, covers the fire like blanket and also brings down the temperature of fuel. Since the contact between the fuel and oxygen is cut off, the fire is controlled.
• It is difficult to burn a heap of green leaves but dry leaves catch fire easily. Explain. Ans. To burn a heap of green leaves is difficult, because its ignition temperature is high, but dry leaves catch fire easily as its ignition temperature switches to low.
• Which zone of a flame does a goldsmith use for melting gold and silver and why? Ans. A goldsmith uses the outermost zone of a flame for melting gold and silver because it is the hottest zone of the flame (temperature $800^{\circ }\mathrm{C}$ ) and is nonluminous in nature.
• In an experiment, 4.5 kg of a fuel was completely burnt. The heat produced was measured to be $180,000\mathrm{kJ}$. Calculate the calorific value of the fuel. Ans. The calorific value of the fuel: Calorific value $=\mathrm{kJ}/\mathrm{kg}=180,000/4.5$ $\mathrm{kJ}/\mathrm{kg}=40,000\mathrm{kJ}/\mathrm{kg}$.
• Can the process of rusting be called combustion? Discuss? Ans. Combustion is a chemical process in which substance reacts with oxygen to give heat and light. In rusting, metal reacts with oxygen to form oxide. But it takes a long time for iron to rust, it doesn't happen immediately. So, we can say that Rusting is an example of slow combustion. In rusting, very small amount of heat is produced and no light is produced.
• 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. Ramesh's water will get heated in a shorter time, because he kept it in the hottest zone.

EXERCISE-01

Multiple choice questions

• The heat and light comes from burning materials known as (1) fire (2) fuel (3) flame (4) all of these
• Which of the following are produced by nuclear reactions? (1) Sun light (2) Heat (3) Light (4) All of these
• Incomplete combustion of fuels gives (1) ${\mathrm{CO}}_2$ gas (2) CO gas (3) $\mathrm{CO}+{\mathrm{H}}_2$ (4) None of these
• The substances which have very low ignition temperature and can easily catch fire with a flame are called (1) luminous substances (2) combustible substances (3) inflammable substances (4) all of these
• Glass is (1) non-combustible (2) combustible (3) supporter of combustion (4) all of these
• The conditions which are required for combustion to take place are (1) fuel (2) ignition temperature (3) oxygen (4) all of these
• Which of the following is not a necessary condition of combustion? (1) Presence of combustible substance. (2) Presence of a supporter of combustion. (3) Attainment of ignition temperature of the fuel. (4) Presence of carbon dioxide.
• Which one of the following is a noncombustible substance? (1) Coal (2) Iron (3) Straw (4) Wood
• For combustion reactions, (1) air is essential (2) combustible substance is essential (3) both (1) and (2) (4) none of these
• Which gas is the best extinguisher? (1) ${\mathrm{CO}}_2$ (2) CO (3) Water vapour (4) None of these
• How fire can be put off? (1) By throwing water on it. (2) By using fire extinguishers. (3) By throwing sand or soil over it. (4) Any of these methods.
• Water cannot be used in (1) Oil fire (2) Forest fire (3) Building fire (4) All of these
• Which is not used as a fire extinguisher? (1) Water (2) Carbon dioxide (3) Oxygen (4) All of the above
• Which of the following fuel burns without a flame? (1) Candle (2) Coal (3) Kerosene oil (4) None of these
• In which zone of a candle flame does complete combustion take place? (1) Inner (2) Outer (3) Middle (4) All three zones
• A luminous flame appears (1) red (2) green (3) yellow (4) blue
• Which zone of the candle flame is hottest? (1) Non-luminous zone (2) Dark zone (3) Luminous zone (4) None of these
• Which is a zone of no combustion? (1) Blue zone (2) Dark zone (3) Luminous zone (4) All of the above
• Dark zone is (1) visible (2) invisible (3) green in colour (4) None of these
• Which fuels are used for running automobiles? (1) Cow dung (2) Petrol (3) Diesel (4) Both (2) and (3)
• Which of the following fuel is used in a thermal power generation? (1) Coal (2) CNG (3) Petrol (4) All of these
• The zone that produces light in the candle flame is (1) non-luminous zone (2) luminous zone (3) dark zone (4) all zones give light
• Which of the following is not the attribute of a good fuel? (1) Low calorific value. (2) Moderate rate of combustion. (3) Fairly cheap and easily available. (4) Safe to handle, store, and transport.
• Which fuel among the following has the highest calorific value? (1) Wood (2) Coal (3) Kerosene (4) LPG
• Burning of LPG is (1) incomplete combustion (2) rapid combustion (3) slow combustion (4) none of these

True or False

• Alcohol, CNG and LPG are inflammable substances.
• Burnt fuel should always leave some residue.
• Wood is a combustible substance.
• Presence of a combustible substance is not essential for a substance to burn.
• Oxygen is a supporter of combustion.
• Combustion cannot take place in the sun since there is no air in the sun.
• Burning of crackers in air is a spontaneous combustion.
• Coal is an inflammable fuel.
• Usually substances catch fire at one fixed temperature.
• The substances which have very high ignition temperature are called inflammable substances.
• Burning of LPG is slow combustion.
• The combustion in which a substance burns rapidly and produces heat and light is called rapid combustion.
• Wood gas burns with a flame.
• Gases or vapours burn with a flame.
• There is a blue colour zone at the base of the wick.
• Blue zone of a candle flame is the coolest.
• Incomplete combustion of wax vapours take place in the outer zone of the candle flame.
• The outer zone of the candle flame is also known as luminous zone.
• Water and sand can be used to extinguish all types of fire.
• Acids rain is very useful for the crops, buildings and soil.
• At airport and petrol pump soda acid fire extinguishers are not used.
• Calorific value of coke (28000-31000 kJ ) is more than that of coal (1500027000 kJ ).
• Carbon monoxide is produced during incomplete combustion of hydrocarbon fuels.
• All the fuels burn with flame.
• Combustion is a chemical process in which a substance reacts with oxygen to give off heat.

Fill in the blanks

• On burning, solid fuels leave and .
• Flame propagation is explained by two theories and . .
• ___and ___are non-combustible substances.
• Substances that burn easily are called- substances.
• Fuel must be heated to its before its starts burning.
• substances have a low ignition temperature.
• Fire produced by oil cannot be controlled by .
• Combustion is of types.
• The combustion in which gas burns rapidly is known as combustion.
• wax burns in a candle flame.
• Burning of white phosphorus is an example of combustion.
• Respiration is a type of combustion.
• A candle flame consists of important zones.
• The innermost zone of flame is known as
• Combustion does not take place in the zone of the candle flame.
• A liquid fuel used in home is .
• Fuels are compounds of and .
• A gaseous fuel nowadays greatly in use is _.
• Burning of wood and coal causes of air.
• A good fuel should have ignition temperature.

Match the column

Crossword puzzle

Across

• A chemical process in which a substance reacts with oxygen to give off heat.
• Ignition temperature is also called as temperature.
• It is a supporter of combustion.
• It is used in soda-acid fire extinguisher as a raw material.
• The type of combustion which requires no external heat.

Down

• The substances which have very low ignition temperature and can easily catch fire with a flame.
• The combustion in which a large amount of gases are evolved with heat, light and sound.
• A region of burning gases.
• Non-luminous zone is the part of a candle flame.
• SPM constitute of fine unburnt carbon particles.

ANSWER KEY

Multiple choice questions

True or False

Fill in the blanks

Match the column

• (1) $\to$ (x), (2) $\to$ (i), (3) $\to$ (viii), (4) $\to$ (ii), (5) $\to$ (iii), (6) $\to$ (ix), (7) $\to$ (iv), (8) $\to$ (v), (9) $\to$ (vi), (10) $\to$ (vii).
• (1) $\to$ (iv), (2) $\to$ (v), (3) $\to$ (i), (4) $\to$ (ii), (5) $\to$ (iii)
• (1) $\to$ (i), (2) $\to$ (vi), (3) $\to$ (ii), (4) $\to$ (v), (5) $\to$ (iv), (6) $\to$ (iii)

Crossword puzzle

EXERCISE-02

Very short answer type questions

• What is a combustible substance?
• When a substance is burnt in the presence of oxygen, what is the phenomenon known as?
• What kind of substances are paper, wood and kerosene?
• Name two non-combustible substances.
• Name two combustible substances.
• What will happen if air supply is stopped to a burning substance?
• Name two inflammable substances.
• Write the name of essential requirements for producing fire?
• What is an inflammable substance?
• When a substance catches fire, what is that temperature known as?
• Name two liquids which have low ignition temperature.
• In which season dry grass catches fire?
• What is a fire extinguisher?
• What happens to natural gas when it is burnt?
• What type of combustion takes place when the food you've eaten is used to provide energy for your body?
• What is the colour of the innermost zone of a candle flame?
• What is the composition of the head of a matchstick?
• What is a primary fuel?
• Which fuel are you using at home?
• What is that substance known as which burnt to use its heat energy?
• What is that value on which the efficiency of a fuel is determined?
• What is power generated by the heat produced by burning fuel?
• Why LPG produce more heat than other fuel?
• Which gas is evolved after burning of coal and diesel?
• Which gas is evolved in incomplete combustion?

Short answer type questions

• Differentiate between luminous and non-luminous flame?
• What is the difference between a combustible and non-combustible substance?
• What are the three conditions necessary for combustion?
• Why doesn't wet wood burn easily?
• What do you mean by ignition temperature of a substance?
• How does a forest catch fire?
• What really is an explosion?
• Differentiate between rapid and slow combustion.
• Why do some substances produce flame?
• Name the petroleum product used for making candles.
• What happens to the wax when a candle is burnt? Is it possible to get this wax back?
• What is the middle zone of a burning candle known as? Why?
• Describe the various zones of a candle flame.
• Differentiate between solid and liquid fuels.
• Why is domestic fuel known as LPG? What do the letters stand for?
• Write four characteristics of an ideal fuel.
• State any two reasons when you consider a particular fuel best.
• Mention any two cost effective ways of cooking.
• What do you mean by calorific value?
• Hydrogen has the highest calorific value. Still, it cannot be used for domestic cooking purposes. Why?

Long answer type questions

• Petrol does not catch fire on its own at room temperature. Why?
• Wet paper does not burn while a dry paper catches fire easily. Why?
• A wet cotton handkerchief soaked in alcohol will not catch fire even it is set fire to? Why?
• Describe the different types of combustion, giving suitable examples.
• What is slow combustion? Explain with at least two suitable examples supported by equations representing the reaction.
• Draw a well labelled diagram of structure of flame.
• What is the characteristic of a 'good' fuel?
• Discuss the various type of gaseous fuels.
• How can we best manage energy sources?
• Write a short note on harmful effects of burning fuel.

Exercise - 01 Solutions

Multiple choice questions

• Option (2) The substances, produce heat & light, in presence of oxygen is known as fuel.

• Option (4) Nuclear reactions produce heat light and solar energy.
• Option (2) In incomplete combustion carbon combines with oxygen to form carbon monoxide gas.
• Option (3) The substance which have very low ignition temperature and can easily catch fire with a flame are called Inflammable substances.
• Option (1) Non - Combustible substance is substance which does not burn. Glass is non-combustible (does not catch fire) substance.
• Option (4) There are three conditions required for combustion. (1) Combustible substance (2) Right ignition temperature (3) Presence of Oxygen
• Option (4) ${\mathrm{CO}}_2$ is non - supporter of combustion.
• Option (2) Iron has a very high ignition temperature around $1450^{\circ }\mathrm{C}$, only at that temp. combustion of iron takes place.
• Option (3) For combustion reactions, air and combustion substance both are essential.
• Option (1) The ${\mathrm{CO}}_2$ considered the best fire extinguisher to put off fire caused by burning of inflammable liquid such as petrol or oil because ${\mathrm{CO}}_2$ stops the influence of oxygen.
• Option (4) Fire can be extinguished by using water, ${\mathrm{CO}}_2$, sand or soil etc.
• Option (1) Water cannot be used in oil fire because oil is lighter, it remains above water and continues burning.
• Option (3) Oxygen gas is supporter of combustion.
• Option (2) Coal burns without a flame.
• Option (2) Outer zone: This zone is blue in colour. It is the hottest part of the flame, because complete combustion due to availability of oxygen.
• Option (3) In Luminous zone of flame, hydrogen burns with brilliant yellow flame.
• Option (1) Non-luminous zone is zone of complete combustion. It is the hottest zone of the candle flame and does not produce much light.
• Option (2) Dark zone as this zone does not support burning because there is no supply of air.
• Option (1) The innermost zone of candle flame is black in colour. It is where incomplete combustion take place.
• Option (4) Petrol, Diesel and CNG are some fuels on which automobiles run.
• Option (1) Coal is used in thermal power plants for electric power generation.
• Option (2) Luminous zone produces yellow light in the candle flame.
• Option (1) A good fuel should have a high calorific value (large amount of heat should be generated).
• Option (4) LPG has the highest calorific value. LPG has a typical specific calorific value of $46100\mathrm{kJ}/\mathrm{kg}$.
• Option (2) LPG burns rapidly and produces heat and light.

True or False

• True Alcohol, CNG and LPG are inflammable substances.
• False An ideal fuel should not leave residue.
• True Wood burns in air and it is a combustible substance.
• False One of the primary requirements for combustion is the presence of combustible material.
• True Combustion is a chemical process in which a substance reacts rapidly with oxygen and gives off heat.
• True Sun also produces heat and light, but there is no oxygen in space. So, sun cannot undergo combustion to produce heat and light.
• False The burning of crackers occurs with the production of huge amounts of heat and light and sound. So it is an example of an explosion.
• True Coal is an flammable fuel because it does not produce any flame. Coal passes high ignition temperature.
• False Different combustible substance catch fire at different temperature. A combustible substance cannot catch fire or burn if its temperature is lower than its ignition temperature.
• False Substances with low Ignition temperature are inflammable.
• False LPG catches fire rapidly, so it's a rapid combustion.
• True Ex-Burning of petrol, LPG.
• True Wood has volatile matter; therefore, it catches fire and produces flame.
• True Gaseous fuels are volatile thus burn with flame.
• True Vaporised wax burns completely.
• False Dark zone is the coolest zone.
• False Outer zone has sufficient supply of oxygen so complete combustion occurs at this zone.
• False Outer zone is non-Luminous zone.
• False Fire caused by oil, can be extinguished by ${\mathrm{CO}}_2$ gas.
• False Acids rain is very harmful for the crops, buildings and soil.
• True Hydrocarbon fire extinguishers are used at airport and petrol pump.
• True Calorific value of coke (28000-31000 kJ) is more than that of coal (15000-27000 kJ).
• True Carbon monoxide are produced during incomplete combustion of hydrocarbon fuels.
• False No, all the fuels do not burn with flame. eg- coal
• True Combustion is a chemical process in which a substance reacts with oxygen to give off heat.

Exercise - 02 Solutions

Very short answer type questions

• A substance which can undergo combustion is called as combustible substance. Example: - Wood, Kerosene
• When a substance is burnt in presence of oxygen, the phenomenon is called as combustion.
• Paper, wood and kerosene are combustible substances.
• Two non - combustible substances are glass and stone.
• Two combustible substances are paper and charcoal.
• If air supply to a burning substance is stopped, the process of burning will stop.
• Two inflammable substances are petrol and LPG.
• The essential requirements for producing fire. (1) Presence of a combustible substance. (2) Presence of oxygen (Supporter of combustion in air) (3) Presence of right ignition temperature.
• The substances which have very low ignition temperature and can easily catch fire are inflammable substances. example - Petrol.
• The temperature at which a substance catches fire is called as ignition temperature or kindling temperature.
• Two liquids with low ignition temperature are - Petrol and kerosene.
• Dry grass catches fire in summer season.
• A fire extinguisher is a device used to control fire.
• When natural gas is burnt it produces heat and light.
• When food in body is used to provide energy, it is a case of slow combustion process.
• The colour of the innermost zone of a candle flame is black.
• Antimony trisulphide and potassium chlorate.
• A fuel in its natural state is called as a primary fuel.
• The fuel used at home is LPG (Liquified Petroleum Gas).
• The substances burnt to produce heat energy is known as Fuel.
• The efficiency of a fuel is determined by its calorific value.
• Power generated by heat produced by burning fuel is Electric power.
• LPG produces more heat than other fuels because it is a gaseous fuel and has a high calorific value.
• The gas evolved is sulphur dioxide.
• Incomplete combustion produces carbon monoxide gas.

Short answer type questions

• Luminous flame is the region of flame formed due to incomplete burning of carbon. In this region, hydrogen burns with brilliant yellow flame. Non - Luminous flame is blue flame and hottest part of flame where complete oxidation (burning) of the fuel takes place.
• Combustible substance is a substance which can undergo combustion. example - Petrol, Kerosene. Non - Combustible substance - A substance which cannot undergo combustion. Example: - Iron, Nails, Glass
• There conditions necessary for combustion are - (1) Combustible substance (2) Air or oxygen (3) Ignition temperature
• Wet wood doesn't burn easily because the water present in the wood absorbs the heat energy, as a result ignition temperature of a wood do not achieve.
• The minimum temperature required for burning a combustible substance before it catches fire is called as ignition temperature.
• During extreme heat in summers the grass and fallen leaves are extremely dry. If there is a tiny spark by rubbing of stone or lightening, they catch fire. The fire spreads very rapidly to trees and to the entire forest.
• The combustion in which large amount of gases are evolved with the production of a tremendous amount of heat, light and sound is called explosion.
• Rapid combustion is the combustion in which a fuel burns rapidly and produces heat and light. Ex. Burning of petrol, LPG. Slow Combustion is the process in which combustion occurs at a very slow pace. ex. Combustion of food in our body.
• Some substance produce flame because they contain gaseous substance or volatile matter which burn easily.
• Petroleum product used for making candles is - paraffin wax.
• When a candle is burnt, some wax melts while some wax burns. It is possible to get back the wax that has melted but not the wax which has undergone burning.
• The middle zone of a burning candle is known as Luminous zone. It is because in this region of the flame hydrogen burns with a brilliant yellow luminous flame.
• Structure of a flame In order to understand the structure of a flame, light a wax candle and watch its flame. Carefully note the different coloured zones in the flame. Starting from the base of the flame, a flame has four zones. (1) Blue zone : It is near the base of the flame. Vaporised wax gets oxidised to carbon monoxide and carbon monoxide burns completely with a blue flame in this zone. (2)Dark inner zone: Surrounding the wick is the dark zone. There is no burning in this zone. If we pass a wooden splinter through the dark zone of the flame, it comes out unscratched (unburnt) showing that there is no 'burning' in this zone. However, some unburnt wax vapours are present in this zone. (3) Luminous zone: In this region of the flame hydrogen burns with a brilliant yellow luminous flame. Burning hydrogen combines with oxygen to form water vapour. Carbon also burns in this zone giving some luminosity to the flame and producing carbon dioxide. Some unburnt carbon particles are left which give rise to soot. (4) Outermost non-luminous zone : This zone is poorly visible and is slightly blue. It is the hottest part of the flame where complete oxidation (burning) of the fuel is taking place.

• Zones of a flame.
• Classification of fuels On the basis of physical state, fuels are classified into three parts. (1) Solid fuels: The fuels which occur in a solid state at room temperature are called solid fuels. Example: Wood, agricultural residues, charcoal, coal, coke, etc. (2) Liquid fuels: The fuels which occur in a liquid state at room temperature are called liquid fuels. Example: Liquified hydrogen, petrol, oil, kerosene, diesel, etc.
• LPG stands for liquified Petroleum Gas. Petroleum Gas obtained by Fractional distillation of petroleum is liquified under high pressure, stored in cylinders and used for cooking as a domestic fuel.
• Ideal Fuel There is probably no fuel that could be considered as an ideal fuel. We should look for a fuel which fulfils most of the requirements for a particular use. Characteristics of a good fuel (1) It should be cheap and readily available. (2) It should be easy to store. (3) It should burn at a moderate rate and its combustion should be controllable. (4) It should have moderate ignition temperature. (5) It should produce very small amount of residues such as ash. (6) It should have large calorific value. (7) It should not produce gases which pollute the air. (8) It should not produce any hazards during transportation.
• A particular fuel is best if (1) It has a high calorific value. (2) It should not cause much pollution.
• Two cost effective ways of cooking are: (a) Use of pressure cooker for cooking to reduce consumption of LPG. (b) Use of alternate sources of energy such as - solar energy, Biogas etc. instead of LPG.
• The amount of heat energy produced on completely burning of one Kilogram of fuel in oxygen is called the calorific value of a fuel.
• Hydrogen has the highest calorific value but cannot be used for domestic cooking purpose because it is highly inflammable in nature.

Long answer type questions

• Petrol is a combustible substance but does not catch fire on its own at room temperature because it requires some heat to raise the temperature upto its ignition temperature so that it catches fire and starts burning.
• Wet paper does not burn while a dry paper catches fire easily because in wet paper, the water present absorbs the heat energy as a result ignition temperature not achieve.
• A wet cotton handkerchief soaked in alcohol will not catch fire because the water present absorbs the heat energy and as a result ignition temperature of handkerchief do not attain hence it do not catches fire.
• Types of combustion Combustion is mainly of three types (1) Rapid combustion (2) Spontaneous combustion (3) Explosion (1) Rapid combustion : The combustion in which the gas burns rapidly and produces heat and light is called rapid combustion. For example : When a burning matchstick is brought near a gas burner and the gas tap is opened, the gas immediately starts burning with the production of heat and light. Eg. Petrol, LPG, spirit, etc., (2)Spontaneous combustion : The combustion in which no external heat is given is known as spontaneous combustion. For example : Burning of white phosphorus in air. (3) Explosion : The combustion in which large amount of gases are evolved with the production of a tremendous amount of heat, light and sound is called explosion. For example : When a cracker is ignited, a sudden reaction, oxidation process takes place, and in which at high speed large amount of gas is evolved with the production of tremendous amount of heat, light and sound.
• The combustion reactions which take place slowly and give less amount of heat are termed as slow combustion. Examples :- (1) Combustion of food in our body. (2) Rusting of iron.
• Structure of a flame In order to understand the structure of a flame, light a wax candle and watch its flame. Carefully note the different coloured zones in the flame. Starting from the base of the flame, a flame has three zones. (i) Inner most zone : It is cooler than outer zones and it is dark. (ii) Middle zone : It is the largest zone of candle flame. This zone gives soot and smoke. (iii) Outermost zone : This zone of the flame is thin and blue in colour. This is the hottest zone of the flame. The temperature of this zone is maximum around $1800^{\circ }\mathrm{C}$.

• zones of flame
• Characteristics of a good fuel (1) It should be cheap and readily available. (2) It should be easy to store. (3) It should burn at a moderate rate and its combustion should be controllable. (4) It should have moderate ignition temperature. (5) It should produce very small amount of residues such as ash. (6) It should have large calorific value. (7) It should not produce gases which pollute the air. (8) It should not produce any hazards during transportation.
• Various types of gaseous fuels. Examples: - Methane $\left({\mathrm{CH}}_4\right)$, LPG (Butane), CNG, Biogas and Hydrogen. (1) Gaseous Fuels have a high calorific value.

(2) Gaseous fuels burn easily with a flame (highly inflammable). (3) Gaseous fuels are less polluting i.e., produce almost no smoke and have no residue on burning. Hence, they are called as clean fuels. (4) LPG is preferred domestic fuel. (5) Public transport is switching to CNG. 9. Management of energy sources: - (1) Effective usage of alternative sources of energy. (a) Use of solar energy or biogas to cook food. (b) Use of hydel or wind energy for electric power generation. (2) Use of pressure cooker for cooking food to reduce wastage of domestic fuel. (3) Switch off the electrical equipment's when not in use. (4) Switch off the engine at stop signals. (5) Proper maintenance of vehicles to reduce unnecessary expenditure of fuel. 10. Harmful effects of burning fuels: - The increasing fuel consumption has harmful effects on the environment. The main products formed during the fuel combustion which produce harmful effect are: 1.Carbon fuels like wood, coal, petroleum release unburnt carbon particles. These fine particles are dangerous pollutants causing respiratory disease, such as asthma. 2.Incomplete combustion forms carbon monoxide gas. It is very poisonous gas. It is dangerous to burn coal in a closed room. The carbon monoxide gas produced can kill persons sleeping in that room. 3.Combustion of most fuels' releases carbon dioxide in the environment. Increased percentage of carbon dioxide in the air causes global warming. Global warming is the rise in temperature of the earth. This result in melting of polar glaciers. This leads to rise in sea level and floods in the seacoast. 4.Burning of coal and diesel release sulphur dioxide gas. It is an extremely suffocating and corrosive gas. Sulphur dioxide and nitrogen oxide dissolve in rain water to form acid. Such rain is called acid rain. It is very harmful for crops, buildings and soil. 5.Wood is also used as a fuel. Burning of wood gives a lot of smoke which causes air pollution and is also very harmful for humans. It may lead to many respiratory problems. Cutting of trees for obtaining wood leads to deforestation which is quite harmful to environment. 6.Carbon particles of smoke or the ash get suspended in the air. Excessive amount of them in the air causes breathing problems.

4.0Key Benefits of NCERT Solutions for Class 8 Science Chapter 4

Here are some key advantages of studying Class 8 Science Chapter 4, "Combustion and Flame":

1. Fundamental Concepts: Understanding combustion provides insights into basic chemical reactions, including exothermic processes and the role of oxygen in burning.
2. Real-World Applications: Knowledge of combustion is essential for various real-life applications, such as cooking, heating, and energy production. This chapter helps students relate theoretical concepts to everyday situations.
3. Safety Awareness: Learning about flames and combustion processes raises awareness about fire safety, including the proper handling of flammable substances and the dangers associated with uncontrolled combustion.
4. Environmental Impact: The chapter introduces students to the impact of combustion on the environment, including air pollution and greenhouse gas emissions, fostering a sense of responsibility toward sustainable practices.
5. Experimental Skills: Studying combustion encourages hands-on experiments, enhancing practical skills such as observation, measurement, and data analysis, which are vital in scientific inquiry.
6. Foundation for Advanced Studies: This chapter serves as a stepping stone for more complex topics in chemistry and physics, such as reactions, energy transformations, and thermodynamics, aiding in the development of critical thinking skills.
7. Interdisciplinary Learning: Combustion is a topic that intersects with various fields, including physics (energy transfer) and environmental science (pollution), promoting a holistic understanding of science.
8. Encouraging Curiosity: The phenomena associated with combustion, such as different types of flames and fuels, stimulate curiosity and interest in scientific exploration and experimentation.