Class 8 Combustion and Flame Question and Answers

Class 8 Combustion and Flame Question and Answers


Class 8 Combustion and Flame Question and Answers | NCERT Solutions Class 8 Science | for the students of CBSE / ICSE and all board exams..


Fill in the blanks:

Calorific value refers to the amount of heat produced by burning ………..of a fuel completely. [1 kilogram]

………… and ………do not produce a flame when burned.[Charcoal & Coal]

……… a poisonous gas produced by incomplete combustion of fuels.[ Carbon monoxide] 

The burning of fuel releases ………into the air.[ carbon dioxide]

The calorific value of a fuel is measured in ………..per kilogram. [kilojoules]

Extinguishers containing ……….gas are used to put out electrical fires. [carbon dioxide] 

A small fire can be extinguished by throwing ………or………… on it.[sand or soil]

In the kitchen, a fire can be extinguished by covering the frying pan with a…………or………..[ fire blanket or wet cloth.]

The combustion process requires ……….[air]


Write down the definitions of …



Combustion occurs when a substance reacts with oxygen (of air) to produce heat and light.


Combustible substance:

Combustible substances are those that can burn.


Non-combustible substance:

Noncombustible substances are those that do not burn


Global warming:

Global warming is caused by excess carbon dioxide in the air, which raises the temperature of the atmosphere.


Ignition temperature:

An ignition temperature is the lowest temperature at which a substance starts burning and catches fire.


Inflammable substances:

Inflammable substances have very low ignition temperatures and can catch fire very easily with a flame.


Answer the following questions:-


What are the conditions required for the combustion process?

There are three conditions that are necessary for combustion to take place. These are:

  • The presence of a combustible substance means A substance that can burn
  • Presence of a supporter of combustion like air or oxygen
  • Heating the combustible substance to its ignition temperature


Why the fire produced by burning oil and petrol cannot be extinguished by water?

Water cannot extinguish the fire caused by oil burning. Water is heavier than oil and petrol, so when it is thrown over burning oil/petrol, it settles down. The oil floats on the surface of the water and continues to burn. Thus, fires caused by burning oil will not be extinguished by pouring water over them


Why the fire produced by an electrical short-circuit cannot be extinguished by water?

Water should not be thrown on fires caused by an electrical short-circuit in an electrical appliance or in an electric wire. Water conducts electricity to a certain degree. Therefore, when water is thrown over the burning electrical appliance, it can give an electric shock to the firefighters. As a result, water cannot extinguish fires caused by electricity.


How many types of combustion are there?

There are various types of combustion. The three important types of combustion are:

  • Rapid combustion,
  • Spontaneous combustion, and
  • Explosive combustion

Rapid combustion occurs when a large amount of heat and light are produced in a short period of time. Examples are burning cooking gas, kerosene oil, and burning wax are examples of rapid combustion.

Combustion that occurs on its own is called spontaneous combustion. Examples include white phosphorus burning spontaneously.

Explosive combustion is a combustion reaction in which large amounts of heat, light, and sound are produced very quickly. Examples are fireworks and crackers.


How many types of fuels are there?

There are three types of fuels: Solid fuels, Liquid fuels and Gaseous fuels.

  • examples of solid fuels are: Wood, Charcoal, Coal, and Cow-dung cakes
  • examples of liquid fuels are: Kerosene, Petrol, and Diesel.
  • examples of gaseous fuels are Natural gas, Petroleum gas, Biogas, and Coal gas.


What are the three zones of flame?

A flame consists of three zones they are innermost zone, the middle zone, and the outer zone.

  • The innermost zone of a flame is dark.
  • The middle zone of a flame is yellow.
  • The outer zone of a flame is blue


Define fuel and give examples?

The term fuel refers to a material that produces heat when burned. Fuels include wood, coal, kerosene, petrol, diesel, and natural gas. Fuels provide good heat energy.


What are the Characteristics of an Ideal/good Fuel?

An ideal fuel has the following characteristics:

  • A high calorific value means it produces a lot of heat
  • It has the right ignition temperature.
  • After burning, there are no harmful emissions or residues left behind
  • It is readily available, inexpensive, and easy to transport.


Define Flame and give examples?

A flame is a region in which combustion/burning of gaseous substances is taking place. Some examples of substances that burn by producing flames are LPG, biogas, wax, camphor, magnesium, kerosene oil, and mustard oil.


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