Class 8 Science – Chapter 6: Combustion and Flame

Introduction

Combustion is a very common process in our daily life. Whenever we cook food on a gas stove, burn wood, light a candle, or use petrol in vehicles, combustion is taking place. Combustion is a chemical reaction in which a substance reacts with oxygen and releases heat and light.

In Class 8 Science Chapter 6 “Combustion and Flame”, we study how substances burn, different types of combustion, fuels, flames, and the structure of a flame.

Combustion is very important for human life because it provides energy for cooking, transportation, electricity generation, and industries. However, combustion can also cause problems such as fires and pollution if it is not controlled properly.

1. What is Combustion?

Combustion is a chemical process in which a substance reacts with oxygen and produces heat and light.

The substance that burns is called a combustible substance or fuel.

Definition

Combustion: The process of burning a substance in the presence of oxygen to produce heat and light.

Examples of Combustion

Some common examples are:

Burning of wood
Burning of petrol or diesel in vehicles
Burning of LPG in gas stoves
Burning of coal in thermal power plants
Burning of candles

Example reaction:

Carbon + Oxygen → Carbon dioxide + Heat + Light

2. Conditions Necessary for Combustion

For combustion to occur, three things are necessary:

1. Fuel

Fuel is a substance that burns to produce heat.

Examples:

Wood
Coal
Petrol
Diesel
LPG
Kerosene

2. Oxygen (Air)

Combustion requires oxygen present in the air.

Without oxygen, burning cannot occur.

Example:
If we cover a burning candle with a glass jar, the flame goes out because oxygen inside the jar is used up.

3. Ignition Temperature

The lowest temperature at which a substance starts burning is called ignition temperature.

Example:

Paper catches fire at a certain temperature.
Petrol burns at a lower temperature than wood.

If the temperature is below ignition temperature, the substance will not burn.

3. Inflammable Substances

Some substances catch fire very easily and burn quickly.

These substances are called inflammable substances.

Definition

Inflammable substances: Substances that have very low ignition temperature and catch fire easily.

Examples

Petrol
LPG
Alcohol
Kerosene

Because these substances catch fire quickly, they must be handled carefully.

Example: Petrol pumps display warning signs like “No Smoking” because petrol vapors can easily catch fire.

4. Types of Combustion

Combustion can occur in different ways depending on the speed and conditions of burning.

1. Rapid Combustion

Rapid combustion is a type of combustion in which a substance burns quickly and produces heat and light.

Example:

Burning of LPG in a gas stove.

When a matchstick is brought near LPG gas, it starts burning immediately.

2. Spontaneous Combustion

Spontaneous combustion occurs when a substance catches fire without an external flame.

Example:

White phosphorus catches fire at room temperature.
Coal piles sometimes catch fire due to internal heating.

3. Explosion

Explosion is a very fast combustion reaction that produces a large amount of heat, light, sound, and gases in a very short time.

Examples:

Firecrackers
Bomb explosions
Gunpowder

Explosion releases energy suddenly and can be dangerous.

5. Flames

When substances burn in the gaseous state, they produce a flame.

Definition

Flame: The visible part of fire where gases burn and produce light and heat.

Examples of flames:

Candle flame
LPG flame
Kerosene lamp flame

Some substances burn without flame.

Examples:

Charcoal
Coal

These substances glow but do not produce flame.

6. Structure of a Flame

A candle flame has three different zones.

1. Inner Zone

Characteristics:

Dark in color
Least hot region
Contains unburnt wax vapors

Reason: There is not enough oxygen for complete burning.

2. Middle Zone

Characteristics:

Yellow in color
Moderately hot
Partial combustion occurs

This zone produces soot particles, which glow and give the yellow color.

3. Outer Zone

Characteristics:

Blue in color
Hottest part of the flame
Complete combustion occurs

This zone receives maximum oxygen from air.

Therefore, it produces maximum heat.

7. Why Does a Candle Flame Produce Light?

When wax burns, it forms tiny particles of carbon.

These carbon particles become very hot and glow, producing yellow light.

This is why candle flames appear bright and yellow.

8. Fuel

Fuel is a substance that burns to produce energy.

Examples of Fuels

Wood
Coal
Petrol
Diesel
LPG
Natural gas
Biogas

Fuels are very important because they provide energy for:

Cooking
Transportation
Industries
Electricity production

9. Characteristics of a Good Fuel

A good fuel should have the following properties:

High calorific value
Easily available
Cheap
Easy to store and transport
Produces little smoke
Safe to use

Examples of good fuels:

LPG
CNG
Natural gas

10. Calorific Value

The calorific value of a fuel is the amount of heat energy produced when 1 kg of fuel burns completely.

Unit of Calorific Value

The unit is kilojoule per kilogram (kJ/kg).

Example:

Fuel	Calorific Value
Cow dung cake	6000–8000 kJ/kg
Wood	17000–22000 kJ/kg
Coal	25000–33000 kJ/kg
Petrol	45000 kJ/kg
LPG	55000 kJ/kg

Higher calorific value means more energy production.

11. Harmful Effects of Burning Fuels

Burning fuels releases gases that cause pollution.

1. Carbon Monoxide (CO)

Incomplete combustion produces carbon monoxide.

It is a poisonous gas.

Breathing carbon monoxide can cause:

Headache
Suffocation
Death in extreme cases

2. Carbon Dioxide (CO₂)

Burning fuels releases carbon dioxide.

Too much carbon dioxide causes global warming.

3. Oxides of Nitrogen and Sulphur

These gases cause:

Acid rain
Air pollution
Breathing problems

12. Global Warming

Global warming occurs when carbon dioxide traps heat in the atmosphere.

This increases the temperature of the Earth.

Effects include:

Melting of glaciers
Rising sea levels
Climate change
Extreme weather

Therefore, we must reduce fuel consumption and use clean energy sources.

13. Fire and Fire Control

Fire occurs when combustion happens uncontrollably.

Three things are necessary for fire:

Fuel
Oxygen
Heat

This is called the Fire Triangle.

If any one of these is removed, fire stops.

14. How to Control Fire

Different fires require different methods.

1. Removing Fuel

Example: Turning off gas supply during a gas fire.

2. Removing Oxygen

Example: Covering fire with sand or blanket.

3. Lowering Temperature

Example: Pouring water to cool down fire.

15. Fire Extinguishers

Fire extinguishers are devices used to control small fires.

Types of Fire Extinguishers

1. Water Fire Extinguisher

Used for:

Wood fires
Paper fires

Not used for electrical fires.

2. Carbon Dioxide (CO₂) Extinguisher

Used for:

Electrical fires
Petrol fires

CO₂ removes oxygen around the fire.

3. Dry Powder Extinguisher

Used for:

Gas fires
Petrol fires
Electrical fires

16. Precautions to Prevent Fire

Some safety measures include:

Do not play with matches.
Do not store petrol near fire.
Switch off gas stove after use.
Check electrical wiring regularly.
Keep fire extinguishers in buildings.

17. Importance of Combustion

Combustion plays an important role in modern life.

Uses

Cooking food
Running vehicles
Generating electricity
Industrial processes
Heating homes in cold regions

However, excessive combustion causes pollution, so we must use energy wisely.

Conclusion

Combustion is a very important chemical process that provides energy for many activities in daily life. In this chapter, we learned that combustion requires fuel, oxygen, and ignition temperature. Different types of combustion include rapid combustion, spontaneous combustion, and explosion.

We also studied the structure of a flame, the properties of good fuels, and the concept of calorific value. While combustion provides energy, it also causes air pollution and global warming if fuels are burned excessively.

Therefore, it is important to use clean fuels like LPG, CNG, and renewable energy sources and follow safety measures to prevent fires.

Class 8 Science (CBSE)

Chapter 6: Combustion and Flame

80 Multiple Choice Questions (MCQ)

1 – 10 MCQ

Combustion is the process of
A. Freezing
B. Burning
C. Melting
D. Boiling
Answer: B
A substance that burns to produce heat is called
A. Metal
B. Fuel
C. Mineral
D. Gas
Answer: B
The gas necessary for combustion is
A. Nitrogen
B. Oxygen
C. Hydrogen
D. Carbon dioxide
Answer: B
The lowest temperature at which a substance catches fire is called
A. Ignition temperature
B. Boiling point
C. Melting point
D. Room temperature
Answer: A
Which of the following is a fuel?
A. Sand
B. Wood
C. Stone
D. Glass
Answer: B
LPG stands for
A. Liquid Petroleum Gas
B. Liquefied Petroleum Gas
C. Liquid Power Gas
D. Light Petroleum Gas
Answer: B
Burning of wood is an example of
A. Combustion
B. Condensation
C. Freezing
D. Evaporation
Answer: A
Which fuel is used in gas stoves?
A. Coal
B. LPG
C. Petrol
D. Diesel
Answer: B
Which of the following burns without flame?
A. Candle
B. LPG
C. Charcoal
D. Kerosene
Answer: C
A substance that catches fire easily is called
A. Inflammable substance
B. Non-metal
C. Element
D. Solid
Answer: A

11 – 20 MCQ

Which of the following is an inflammable substance?
A. Petrol
B. Sand
C. Glass
D. Stone
Answer: A
Fire requires
A. Oxygen
B. Fuel
C. Heat
D. All of these
Answer: D
The unit of calorific value is
A. Joule
B. Kilojoule/kg
C. Meter
D. Newton
Answer: B
The hottest zone of a candle flame is
A. Inner zone
B. Middle zone
C. Outer zone
D. Dark zone
Answer: C
The yellow part of the candle flame is
A. Inner zone
B. Middle zone
C. Outer zone
D. Invisible zone
Answer: B
The innermost zone of flame is
A. Dark
B. Blue
C. Yellow
D. White
Answer: A
Explosion produces
A. Sound
B. Heat
C. Light
D. All of these
Answer: D
Burning of crackers is an example of
A. Rapid combustion
B. Explosion
C. Spontaneous combustion
D. Slow combustion
Answer: B
Which fuel has high calorific value?
A. Cow dung cake
B. LPG
C. Wood
D. Paper
Answer: B
Which gas causes global warming?
A. Oxygen
B. Carbon dioxide
C. Hydrogen
D. Nitrogen
Answer: B

21 – 30 MCQ

Incomplete combustion produces
A. Carbon monoxide
B. Oxygen
C. Nitrogen
D. Hydrogen
Answer: A
Carbon monoxide is
A. Poisonous
B. Harmless
C. Useful
D. Colorful
Answer: A
A good fuel should produce
A. More smoke
B. Less heat
C. Less pollution
D. Bad smell
Answer: C
Coal burns with
A. Flame
B. No flame
C. Blue flame
D. Green flame
Answer: B
Which of the following is used to extinguish fire?
A. Water
B. Sand
C. Fire extinguisher
D. All of these
Answer: D
The main component of natural gas is
A. Methane
B. Oxygen
C. Nitrogen
D. Hydrogen
Answer: A
Which fuel is used in vehicles?
A. Petrol
B. Diesel
C. CNG
D. All of these
Answer: D
CNG stands for
A. Compressed Natural Gas
B. Chemical Natural Gas
C. Cold Natural Gas
D. Carbon Natural Gas
Answer: A
Which fuel causes least pollution?
A. Coal
B. Petrol
C. CNG
D. Wood
Answer: C
Burning of magnesium ribbon produces
A. Bright white flame
B. Blue flame
C. Yellow flame
D. No flame
Answer: A

31 – 40 MCQ

Fire can be controlled by
A. Removing oxygen
B. Removing fuel
C. Cooling temperature
D. All of these
Answer: D
Which fire extinguisher is used for electrical fire?
A. Water
B. CO₂
C. Sand
D. Foam
Answer: B
Wax of candle melts due to
A. Heat
B. Cold
C. Wind
D. Light
Answer: A
Wax vapors burn in
A. Flame
B. Water
C. Air only
D. Vacuum
Answer: A
Combustion is a
A. Physical change
B. Chemical change
C. Mechanical change
D. Temporary change
Answer: B
Which fuel has the lowest calorific value?
A. LPG
B. Petrol
C. Cow dung cake
D. Diesel
Answer: C
Which gas supports burning?
A. Nitrogen
B. Oxygen
C. Carbon dioxide
D. Helium
Answer: B
Global warming is caused mainly by
A. Carbon dioxide
B. Oxygen
C. Nitrogen
D. Hydrogen
Answer: A
Acid rain is caused by
A. Oxygen
B. Nitrogen oxide and sulphur dioxide
C. Hydrogen
D. Carbon monoxide
Answer: B
Burning of petrol is an example of
A. Rapid combustion
B. Explosion
C. Spontaneous combustion
D. Slow combustion
Answer: A

41 – 50 MCQ

Which zone of flame has complete combustion?
A. Inner zone
B. Middle zone
C. Outer zone
D. None
Answer: C
The color of outer flame is
A. Blue
B. Yellow
C. Red
D. Green
Answer: A
The yellow color of flame is due to
A. Oxygen
B. Carbon particles
C. Nitrogen
D. Hydrogen
Answer: B
Fire triangle includes
A. Fuel
B. Oxygen
C. Heat
D. All of these
Answer: D
Which fuel is used in power plants?
A. Coal
B. Petrol
C. LPG
D. Kerosene
Answer: A
Which fuel is used in aeroplanes?
A. Petrol
B. Kerosene
C. Coal
D. Wood
Answer: B
A substance that does not burn is called
A. Combustible
B. Non-combustible
C. Inflammable
D. Fuel
Answer: B
Which of the following is non-combustible?
A. Wood
B. Coal
C. Stone
D. Petrol
Answer: C
Water cannot extinguish
A. Wood fire
B. Paper fire
C. Electrical fire
D. Cloth fire
Answer: C
Fire extinguishers are used in
A. Homes
B. Offices
C. Schools
D. All of these
Answer: D

51 – 60 MCQ

Which of the following produces the most smoke?
A. Coal
B. LPG
C. CNG
D. Hydrogen
Answer: A
LPG is mainly composed of
A. Propane and Butane
B. Methane
C. Hydrogen
D. Nitrogen
Answer: A
Which fuel burns with blue flame?
A. LPG
B. Coal
C. Wood
D. Paper
Answer: A
Which part of flame is coolest?
A. Inner zone
B. Outer zone
C. Middle zone
D. All
Answer: A
Burning of diesel in engine is
A. Combustion
B. Condensation
C. Evaporation
D. Freezing
Answer: A
Explosion occurs due to
A. Rapid release of energy
B. Cooling
C. Freezing
D. Melting
Answer: A
Which gas is used in fire extinguisher?
A. Oxygen
B. Carbon dioxide
C. Hydrogen
D. Nitrogen
Answer: B
Charcoal is obtained from
A. Wood
B. Coal
C. Sand
D. Iron
Answer: A
Which fuel is eco-friendly?
A. Coal
B. Wood
C. CNG
D. Diesel
Answer: C
Burning of candle produces
A. Heat and light
B. Only heat
C. Only light
D. Only smoke
Answer: A

61 – 70 MCQ

The main source of energy on Earth is
A. Moon
B. Sun
C. Wind
D. Water
Answer: B
LPG is stored in
A. Cylinders
B. Tanks
C. Pipes
D. Bottles
Answer: A
Fire can spread quickly due to
A. Wind
B. Water
C. Sand
D. Ice
Answer: A
Which fuel burns cleanly?
A. Coal
B. Wood
C. LPG
D. Cow dung
Answer: C
Which fuel is solid?
A. Coal
B. LPG
C. Petrol
D. Diesel
Answer: A
Which fuel is liquid?
A. Coal
B. Petrol
C. Wood
D. Charcoal
Answer: B
Which fuel is gaseous?
A. LPG
B. Coal
C. Wood
D. Coke
Answer: A
Burning of coal produces
A. Smoke
B. Heat
C. Gas
D. All of these
Answer: D
Petrol pump has sign
A. No Smoking
B. Stop
C. Entry
D. Exit
Answer: A
Which is safest fuel for cooking?
A. Coal
B. LPG
C. Wood
D. Cow dung
Answer: B

71 – 80 MCQ

Which gas is produced during complete combustion?
A. Carbon dioxide
B. Carbon monoxide
C. Hydrogen
D. Nitrogen
Answer: A
Incomplete combustion produces
A. Carbon monoxide
B. Oxygen
C. Hydrogen
D. Nitrogen
Answer: A
Which of the following is renewable fuel?
A. Biogas
B. Coal
C. Petrol
D. Diesel
Answer: A
Which fuel produces least pollution?
A. CNG
B. Coal
C. Diesel
D. Wood
Answer: A
The hottest flame is
A. Blue flame
B. Yellow flame
C. Red flame
D. Green flame
Answer: A
Combustion of fuel releases
A. Heat
B. Light
C. Energy
D. All of these
Answer: D
Coal tar is obtained from
A. Coal
B. Wood
C. Petrol
D. Diesel
Answer: A
The middle zone of flame is
A. Yellow
B. Blue
C. Black
D. White
Answer: A
The outer zone of flame has
A. Complete combustion
B. Incomplete combustion
C. No combustion
D. Partial combustion
Answer: A
Combustion is useful for
A. Cooking
B. Running vehicles
C. Producing electricity
D. All of these
Answer: D

Class 8 Science – Chapter 6: Combustion and Flame

10 Case Study Based Questions

Case Study 1: LPG in Kitchen

Rita’s mother cooks food on an LPG gas stove. LPG burns with a blue flame and produces a large amount of heat. LPG is stored in cylinders and is considered a clean fuel because it produces very little smoke.

Questions

What does LPG stand for?
Why is LPG considered a good fuel?
Which color flame is produced when LPG burns properly?
Name one advantage of LPG over coal.

Case Study 2: Candle Flame

A teacher lit a candle in the classroom to explain the structure of a flame. She showed that the candle flame has three zones: inner zone, middle zone, and outer zone. The outer zone is the hottest part of the flame.

Questions

How many zones are present in a candle flame?
Which zone of the flame is the hottest?
Which zone appears yellow in color?
Why is the inner zone dark?

Case Study 3: Fire in a Forest

During summer, dry leaves in a forest sometimes catch fire due to high temperature. The fire spreads quickly because of wind and dry fuel materials.

Questions

What type of combustion may occur when fire starts without external flame?
Name two conditions necessary for combustion.
Why does fire spread quickly in forests during summer?
Name one method to control forest fire.

Case Study 4: Petrol Pump Safety

Petrol pumps always display a sign saying “No Smoking.” Petrol is a highly inflammable substance and its vapors can catch fire easily.

Questions

What are inflammable substances?
Give one example of an inflammable substance.
Why is smoking prohibited at petrol pumps?
What is the ignition temperature?

Case Study 5: Burning of Crackers

During festivals, people burn firecrackers which produce bright light, sound, and gases. This reaction occurs very quickly and releases a lot of energy.

Questions

What type of combustion occurs in firecrackers?
What is an explosion?
Name one disadvantage of burning crackers.
Which gas released during burning causes air pollution?

Case Study 6: Fuel for Vehicles

Vehicles like cars and buses run on fuels such as petrol, diesel, or CNG. Among these fuels, CNG produces the least pollution and is considered environment-friendly.

Questions

What does CNG stand for?
Which fuel produces the least pollution?
Why are cleaner fuels preferred today?
Name two fuels used in vehicles.

Case Study 7: Fire Extinguishers

In schools and offices, fire extinguishers are installed for safety. Different types of extinguishers are used for different types of fires, such as water, carbon dioxide, and dry powder extinguishers.

Questions

What is the purpose of a fire extinguisher?
Which gas is commonly used in fire extinguishers?
Why should water not be used on electrical fires?
Name two types of fire extinguishers.

Case Study 8: Calorific Value of Fuels

Different fuels produce different amounts of heat when burned. LPG and petrol have high calorific value, while cow dung cake has lower calorific value.

Questions

What is calorific value?
What is the unit of calorific value?
Which fuel produces more energy: LPG or cow dung cake?
Why is high calorific value important for fuels?

Case Study 9: Air Pollution from Fuels

Burning fuels releases gases such as carbon dioxide, carbon monoxide, nitrogen oxides, and sulphur dioxide. These gases pollute the air and cause environmental problems.

Questions

Which gas causes global warming?
Which gas is poisonous and produced by incomplete combustion?
What environmental problem is caused by excessive carbon dioxide?
Name one harmful effect of air pollution.

Case Study 10: Fire Triangle

For fire to occur, three things are required: fuel, oxygen, and heat. These three factors form the fire triangle. Removing any one of these can stop the fire.

Questions

What are the three elements of the fire triangle?
What happens if oxygen supply is cut off?
Why is sand used to extinguish fire?
Name one method to stop a fire.

Class 8 Science – Chapter 6: Combustion and Flame

20 Short Answer Questions

What is combustion?
Combustion is the chemical process in which a substance reacts with oxygen and produces heat and light.
What is a fuel?
A fuel is a substance that burns to produce heat energy.
Define ignition temperature.
Ignition temperature is the lowest temperature at which a substance catches fire and starts burning.
What are inflammable substances?
Substances that catch fire easily because of their low ignition temperature are called inflammable substances.
Give two examples of fuels.
Coal and LPG.
Name three conditions necessary for combustion.
Fuel, oxygen (air), and ignition temperature.
What is rapid combustion?
Rapid combustion is a type of combustion in which a substance burns quickly and produces heat and light immediately.
What is spontaneous combustion?
Spontaneous combustion is the type of combustion in which a substance suddenly catches fire without an external flame.
What is an explosion?
Explosion is a sudden combustion reaction that produces heat, light, sound, and large amounts of gases.
What is a flame?
Flame is the visible part of fire where gases burn and produce heat and light.
Name the three zones of a candle flame.
Inner zone, middle zone, and outer zone.
Which zone of the flame is the hottest?
The outer zone.
Why is the middle zone of flame yellow?
Because of glowing carbon particles formed during incomplete combustion.
Define calorific value of a fuel.
The amount of heat energy produced when 1 kg of fuel burns completely is called calorific value.
What is the unit of calorific value?
Kilojoule per kilogram (kJ/kg).
Name two clean fuels.
LPG and CNG.
Which gas is produced during complete combustion of fuel?
Carbon dioxide.
Which poisonous gas is produced during incomplete combustion?
Carbon monoxide.
What is the fire triangle?
The fire triangle consists of fuel, oxygen, and heat which are required for fire.
Name two methods to control fire.
Removing oxygen (using sand or CO₂) and cooling the fuel (using water).

10 Long Answer Questions

1. What is combustion? Explain the conditions necessary for combustion.

Combustion is a chemical reaction in which a substance reacts with oxygen and produces heat and light. The substance that burns is called fuel.

Three conditions necessary for combustion are:

Fuel: A combustible substance like wood, coal, petrol, or LPG.
Oxygen: Oxygen from air supports the burning process.
Ignition Temperature: The minimum temperature required for a substance to start burning.

If any one of these conditions is not present, combustion cannot occur.

2. Explain the different types of combustion.

There are three main types of combustion:

Rapid Combustion:
A substance burns quickly and produces heat and light immediately.
Example: Burning of LPG in a gas stove.
Spontaneous Combustion:
A substance catches fire on its own without an external flame.
Example: White phosphorus.
Explosion:
A very fast combustion reaction that releases heat, light, sound, and gases.
Example: Firecrackers.

3. Describe the structure of a candle flame.

A candle flame has three zones:

Inner Zone:
Dark in color and least hot. It contains unburnt wax vapors.
Middle Zone:
Yellow in color and moderately hot. Incomplete combustion occurs here.
Outer Zone:
Blue in color and the hottest region. Complete combustion occurs here because plenty of oxygen is available.

4. What are inflammable substances? Give examples.

Inflammable substances are materials that catch fire very easily because they have a low ignition temperature.

Examples include:

Petrol
LPG
Alcohol
Kerosene

These substances must be handled carefully because they can catch fire quickly.

5. What is a fuel? Write the characteristics of a good fuel.

A fuel is a substance that burns to produce heat energy.

Characteristics of a good fuel:

High calorific value
Easily available
Cheap
Produces little smoke
Easy to store and transport
Safe to use

Examples of good fuels are LPG and CNG.

6. What is calorific value? Explain its importance.

Calorific value is the amount of heat produced when 1 kilogram of fuel burns completely.

Unit: kilojoule per kilogram (kJ/kg).

Importance:

Helps compare efficiency of fuels
Higher calorific value means more energy production
Useful in selecting fuels for industries and vehicles

7. Explain the harmful effects of burning fuels.

Burning fuels releases harmful gases that cause pollution.

Carbon monoxide: A poisonous gas produced by incomplete combustion.
Carbon dioxide: Causes global warming.
Nitrogen oxides and sulphur dioxide: Cause acid rain.
Smoke and soot: Cause breathing problems and air pollution.

Therefore, cleaner fuels should be used.

8. What is fire? How can fire be controlled?

Fire is the result of uncontrolled combustion.

Fire can be controlled by removing any one of the three elements of the fire triangle:

Removing fuel: Stop the supply of fuel.
Removing oxygen: Cover fire with sand or blanket.
Cooling: Use water to lower the temperature.

9. Explain the working of fire extinguishers.

Fire extinguishers are used to control small fires.

Types include:

Water extinguisher: Used for wood and paper fires.
Carbon dioxide extinguisher: Used for electrical fires.
Dry powder extinguisher: Used for gas and petrol fires.

These extinguishers work by cooling the fire or cutting off oxygen supply.

10. Write precautions to prevent fire accidents.

Some safety precautions include:

Do not play with matchsticks or fire.
Do not smoke near petrol pumps.
Keep inflammable substances away from fire.
Switch off gas stove after cooking.
Install fire extinguishers in buildings.
Maintain electrical wiring properly.

Following these precautions helps prevent fire accidents.

Class 8 Science (CBSE)

Chapter 6: Combustion and Flame

Test Paper – 80 Marks

Time: 3 Hours
Maximum Marks: 80

Section A – Multiple Choice Questions (1×20 = 20 Marks)

Choose the correct answer.

Combustion is the process of
a) Freezing
b) Burning
c) Melting
d) Condensation
The lowest temperature at which a substance catches fire is called
a) Boiling point
b) Ignition temperature
c) Melting point
d) Room temperature
Which gas supports combustion?
a) Nitrogen
b) Oxygen
c) Carbon dioxide
d) Hydrogen
LPG stands for
a) Liquid Petroleum Gas
b) Liquefied Petroleum Gas
c) Light Petroleum Gas
d) Low Petroleum Gas
Which fuel burns with blue flame?
a) Wood
b) LPG
c) Coal
d) Charcoal
A substance that catches fire easily is called
a) Non-combustible
b) Inflammable
c) Neutral
d) Metal
The hottest part of a candle flame is
a) Inner zone
b) Middle zone
c) Outer zone
d) Dark zone
Incomplete combustion produces
a) Oxygen
b) Carbon dioxide
c) Carbon monoxide
d) Nitrogen
Which gas is responsible for global warming?
a) Oxygen
b) Nitrogen
c) Carbon dioxide
d) Hydrogen
The unit of calorific value is
a) Joule
b) Kilojoule/kg
c) Newton
d) Meter
Which of the following burns without flame?
a) Candle
b) Charcoal
c) LPG
d) Kerosene
CNG stands for
a) Carbon Natural Gas
b) Chemical Natural Gas
c) Compressed Natural Gas
d) Cold Natural Gas
Burning of crackers is an example of
a) Rapid combustion
b) Explosion
c) Spontaneous combustion
d) Slow combustion
Which fuel causes least pollution?
a) Coal
b) Wood
c) CNG
d) Diesel
Fire triangle consists of
a) Heat, water, oxygen
b) Fuel, oxygen, heat
c) Fuel, smoke, heat
d) Heat, sand, fuel
Which gas is used in fire extinguishers?
a) Oxygen
b) Carbon dioxide
c) Hydrogen
d) Nitrogen
Coal is a
a) Solid fuel
b) Liquid fuel
c) Gas fuel
d) Chemical fuel
Which fuel is used in vehicles?
a) Petrol
b) Diesel
c) CNG
d) All of these
Which zone of flame has complete combustion?
a) Inner zone
b) Middle zone
c) Outer zone
d) None
Combustion produces
a) Heat
b) Light
c) Energy
d) All of these

Section B – Short Answer Questions (2×10 = 20 Marks)

Define combustion.
What is ignition temperature?
Name two inflammable substances.
Write two conditions necessary for combustion.
What is a flame?
Name the three zones of a candle flame.
What is calorific value of a fuel?
Name two clean fuels.
What is rapid combustion?
Write two methods to control fire.

Section C – Case Study Questions (4×5 = 20 Marks)

Case Study 1

Ravi’s mother cooks food on an LPG gas stove. LPG burns with a blue flame and produces a large amount of heat. LPG is considered a clean fuel because it produces very little smoke.

What does LPG stand for?
Why is LPG considered a clean fuel?
What color flame is produced by LPG?
Name one advantage of LPG over coal.
Is LPG solid, liquid, or gas fuel?

Case Study 2

A science teacher lit a candle in the classroom to show the structure of a flame. She explained that a candle flame has three zones and the outer zone is the hottest.