Combustion and Flame
Each subtopic includes About section, revision page link, 10 preview questions, and practice CTAs.
Conditions Necessary for Combustion
SubtopicConditions Necessary for Combustion under Combustion and Flame for Grade 8 CBSE.
Preview questions (no answers)
- 1.
In the experimental setup shown in the diagram, a combustible material is heated using a heat source, yet it does not catch fire. Based on the conditions necessary for combustion, what is the most likely reason for this?
A.The material being used is non-combustible.
B.The ignition temperature was not reached.
C.There is no supporter of combustion, such as oxygen.
D.Combustion can only occur in the presence of sunlight.
- 2.
Which of the following is an essential factor to control fire?
A.Increasing the fuel
B.Removing the heat (cooling)
C.Adding more oxygen
D.Increasing the temperature
- 3.
A substance that gives off heat and light during its reaction with oxygen is said to be:
A.Undergoing evaporation
B.Undergoing combustion
C.Undergoing condensation
D.Undergoing freezing
- 4.
Which of the following is a non-combustible material commonly used in construction?
A.Wood
B.Cement
C.Straw
D.Dry leaves
- 5.
Which gas is the most essential supporter of combustion on Earth?
A.Nitrogen
B.Oxygen
C.Helium
D.Carbon dioxide
- 6.
When we rub a matchstick on the side of a matchbox, heat is produced due to:
A.Convection
B.Radiation
C.Friction
D.Chemical decomposition
- 7.
Which of the following describes 'Ignition Temperature' correctly?
A.The maximum temperature a fuel can reach
B.The temperature at which a substance starts to melt
C.The minimum temperature at which a substance catches fire
D.The average temperature of a flame
- 8.
If a large pile of dry hay catches fire, why is it often recommended to spray the surrounding unburned hay with water?
A.To make the hay heavier so the wind doesn't blow it.
B.To increase the ignition temperature of the unburned hay by making it wet and requiring extra heat for evaporation.
C.To turn the hay into compost so it can't burn.
D.To provide a source of drinking water for firefighters.
- 9.
Why do some materials smolder (burn without a flame) while others burn with a flame?
A.Materials that vaporize on heating produce a flame, while those that do not vaporize (like charcoal) only smolder.
B.Smoldering occurs only when the ignition temperature is not reached.
C.Only materials that contain oxygen in their structure produce a flame.
D.Flaming requires a lack of oxygen.
- 10.
Which of the following conditions is violated when a fire is extinguished by throwing sand over it?
A.The fuel is removed.
B.The temperature is raised above the ignition point.
C.The supply of oxygen is cut off.
D.The chemical nature of the fuel is changed to a gas.
Download the worksheet for Combustion and Flame - Conditions Necessary for Combustion to practice offline. It includes additional chapter-level practice questions.
Types of Combustion: Rapid, Spontaneous, and Explosion
SubtopicTypes of Combustion: Rapid, Spontaneous, and Explosion under Combustion and Flame for Grade 8 CBSE.
Preview questions (no answers)
- 1.
Forest fires during very hot summers are mostly due to:
A.Rapid combustion
B.Spontaneous combustion
C.Explosion
D.Slow combustion
- 2.
What is the main difference between an explosion and rapid combustion?
A.Explosion produces sound and gas suddenly
B.Rapid combustion produces sound
C.Explosion happens slowly
D.Rapid combustion produces more gas
- 3.
Rapid combustion usually requires which of the following to start?
A.External heat or spark
B.Sub-zero temperatures
C.Absolute vacuum
D.Absence of oxygen
- 4.
White phosphorus is kept in water because it undergoes ______ in air at room temperature.
A.Rapid combustion
B.Spontaneous combustion
C.Explosion
D.No combustion
- 5.
A student categorized three materials based on their combustion behavior:
- Material 1: Bursts into flames on its own without any external heating.
- Material 2: Burns quickly when lit with a matchstick but produces no loud sound.
- Material 3: Produces a loud bang and a sudden expansion of gas when ignited.
Using the logic in the provided flowchart, which material corresponds to Type Z?
A.Material 1
B.Material 2
C.Material 3
D.None of the materials
- 6.
Which of the following statements about rapid combustion is correct?
A.It takes place at a very slow pace.
B.It produces a huge amount of sound only.
C.The substance burns quickly as long as the heat source is provided or the fuel is available.
D.The substance ignites on its own without any spark.
- 7.
Which of these factors is common to both Rapid and Explosion but NOT typically Spontaneous combustion?
A.Production of heat
B.Presence of a combustible substance
C.Requirement of an initial external ignition source
D.Production of light
- 8.
Which of these is a unique product of an explosion compared to rapid combustion?
A.Heat
B.Light
C.A large volume of gas evolved suddenly
D.Water vapor
- 9.
Which of the following describes the behavior of LPG when a lighter is clicked near it?
A.It undergoes slow oxidation.
B.It undergoes rapid combustion, producing heat and light.
C.It undergoes spontaneous combustion because it is a gas.
D.It undergoes an explosion even if the burner is off.
- 10.
Why does a forest fire often start as spontaneous combustion during a very hot summer?
A.The trees turn into coal.
B.The sun's heat or lightning provides enough energy to reach the ignition temperature of dry leaves.
C.The carbon dioxide in the air becomes flammable at high temperatures.
D.The roots of trees produce methane which explodes.
Download the worksheet for Combustion and Flame - Types of Combustion: Rapid, Spontaneous, and Explosion to practice offline. It includes additional chapter-level practice questions.
Zones of a Candle Flame
SubtopicZones of a Candle Flame under Combustion and Flame for Grade 8 CBSE.
Preview questions (no answers)
- 1.
In a candle flame, the outer zone represents:
A.Partial oxidation
B.Complete oxidation
C.No oxidation
D.Solidification
- 2.
Which zone shows that combustion is taking place in the presence of limited air?
A.Outer zone
B.Middle zone
C.Innermost zone
D.Wick
- 3.
The 'non-luminous' zone of a flame is the ______ part.
A.Innermost
B.Middle
C.Outer
D.Base
- 4.
What provides the heat to initially vaporize the wax in a candle?
A.The matchstick or lighter used to light it
B.The surrounding air
C.The liquid wax
D.The solid wax
- 5.
In which zone is the chemical reaction of wax with oxygen most efficient?
A.Middle zone
B.Innermost zone
C.Outer zone
D.Dark zone
- 6.
Which part of the flame contains the 'unburnt carbon particles' that later form soot?
A.The hottest part
B.The middle luminous part
C.The innermost dark part
D.The blue base
- 7.
Why does a candle flame always point upwards?
A.Because wax is light
B.Due to the gravitational pull on carbon
C.Because hot gases are less dense and rise
D.Due to the magnetic field of the earth
- 8.
Which of the following statements about the 'Non-luminous zone' is FALSE?
A.It is the outermost part of the flame.
B.It is where complete combustion takes place.
C.It is yellow in color due to the presence of carbon particles.
D.It is the hottest part of the flame.
- 9.
The 'blue' color in the non-luminous zone is caused by the presence of short-lived chemical intermediates like and radicals. This process is known as:
A.Incandescence
B.Chemiluminescence
C.Phosphorescence
D.Fluorescence
- 10.
What would happen to the flame if the wick were made of a non-porous material like a solid glass rod?
A.The flame would be very small and blue.
B.The flame would not exist because liquid wax cannot reach the heat zones.
C.The flame would be very smoky.
D.The innermost zone would become the hottest.
Download the worksheet for Combustion and Flame - Zones of a Candle Flame to practice offline. It includes additional chapter-level practice questions.
Fuel Efficiency and Calorific Value
SubtopicFuel Efficiency and Calorific Value under Combustion and Flame for Grade 8 CBSE.
Preview questions (no answers)
- 1.
Which of the following is NOT a fossil fuel?
A.Coal
B.Petroleum
C.Natural Gas
D.Biogas
- 2.
Acid rain is harmful to:
A.Crops
B.Buildings
C.Soil
D.All of the above
- 3.
Calorific value determines the _______ of a fuel.
A.Color
B.Efficiency
C.Mass
D.Temperature
- 4.
Which of these fuels is most likely to cause the most air pollution when burned in an open space?
A.CNG
B.LPG
C.Hydrogen
D.Cow dung cakes
- 5.
Which of these factors does NOT determine the efficiency of a fuel?
A.Calorific value
B.The amount of residue left after burning
C.The color of the fuel before it is burnt
D.The rate of combustion
- 6.
If the calorific value of kerosene is , how much kerosene is needed to produce of heat?
A.B.C.D. - 7.
The calorific value of Biogas is approximately:
A.B.C.D. - 8.
In a comparison between Kerosene (CV ) and Petrol (CV ), petrol is used in cars and kerosene in stoves. What is a key reason for this choice beyond just Calorific Value?
A.Kerosene has a higher ignition temperature and is safer for pressurized stoves.
B.Petrol is much cheaper than kerosene.
C.Kerosene produces no smoke at all.
D.Petrol has a higher calorific value when burned in stoves.
- 9.
Which of the following scenarios would lead to the highest production of Carbon Monoxide?
A.Burning LPG in a well-ventilated kitchen
B.Burning coal in a closed room with no windows
C.Burning dry wood in an open field
D.Burning hydrogen in a specialized laboratory
- 10.
If an engine uses of a fuel with a CV of and produces of mechanical work, what is the thermal efficiency of the engine?
A.B.C.D.
Download the worksheet for Combustion and Flame - Fuel Efficiency and Calorific Value to practice offline. It includes additional chapter-level practice questions.
Harmful Effects of Burning Fuels
SubtopicHarmful Effects of Burning Fuels under Combustion and Flame for Grade 8 CBSE.
Preview questions (no answers)
- 1.
Incomplete combustion occurs when there is:
A.Excess of oxygen
B.Insufficient supply of air/oxygen
C.No fuel present
D.Low temperature
- 2.
Which of the following results from Global Warming?
A.Predictable weather cycles
B.Change in rainfall patterns
C.Growth of more glaciers
D.Increase in polar ice
- 3.
What kind of particles are responsible for causing smog in big cities during winter?
A.Water droplets only
B.Oxygen molecules
C.Smoke and dust particles
D.Nitrogen gas
- 4.
Why is the use of LPG better than burning wood in the kitchen?
A.LPG produces more smoke
B.LPG is a cleaner fuel with no ash residue
C.LPG is harder to burn
D.LPG leads to more deforestation
- 5.
How does the 'Greenhouse Effect' caused by fuel emissions differ from 'Global Warming'?
A.They are the same thing
B.Greenhouse effect is the process; global warming is the resulting increase in temperature
C.Greenhouse effect cools the earth, global warming heats it
D.Greenhouse effect only happens in winter
- 6.
Sulfur dioxide is released into the atmosphere primarily by the combustion of which fuel?
A.Biogas
B.Coal
C.Hydrogen
D.LPG
- 7.
Which of the following fuels is likely to produce the most amount of carbon monoxide if burned in a poorly ventilated kitchen?
A.B.C.Coal
D.Biogas
- 8.
Analyze the following chemical transition. What is the primary harmful effect on human health associated with 'C'?
A.Increased bone density due to carbon absorption.
B.Reduced oxygen-carrying capacity of blood leading to suffocation.
C.Higher energy levels due to excess carbon in cells.
D.Total immunity to respiratory infections.
- 9.
Which phenomenon is most likely to occur in a valley surrounded by hills where many people burn wood and coal for heating during a cold, still night?
A.A 'Temperature Inversion' where smoke and pollutants are trapped near the ground, causing severe respiratory distress.
B.A 'Tornado' caused by the heat of the fires.
C.The conversion of the valley into a tropical rainforest overnight.
D.The immediate neutralization of all atmospheric .
- 10.
How does 'Carbon Monoxide' () affect the central nervous system in cases of non-lethal, chronic exposure from fuel fumes?
A.It speeds up reaction times and makes the brain sharper.
B.It causes symptoms like impaired judgment, memory loss, and fatigue due to chronic low oxygen supply to the brain.
C.It turns the brain into a carbon-based computer.
D.It has no effect on the brain; it only affects the stomach.
Download the worksheet for Combustion and Flame - Harmful Effects of Burning Fuels to practice offline. It includes additional chapter-level practice questions.