Lakhmir Singh Manjit Kaur Class 8 Science 6th Chapter Combustion And Flame Solutions

Lakhmir Singh and Manjit Kaur Class 8 Science 6th Chapter Combustion And Flame Solution

Lakhmir Singh and Manjit Kaur Science solution: Combustion And Flame Chapter 6. Here you get easy solutions of Lakhmir Singh and Manjit Kaur Science solution Chapter 6. Here we give Chapter 6 all solution of class 8. Its help you to complete your homework.

Board – CBSE

Text Book – SCIENCE

Class – 8

Chapter – 6


(1)  The lowest temperature at which a substance catches fire and  stars burning, is called that substance is called its ignition temperature.

(2) Petrol

(3) Water

(4) Carbon di oxide

(5) coal dust

(6)  kilojoules per kilogram (kJ/kg)

(7) Coal

(8) Hydrogen

(9) Calorific value

(10) One solid is Coal, One liquid is petrol and one gas is LPG which burn by producing a flame.

(11) Charcoal

(12) coal

(13) 3

(14) Outer zone.

(15) a> Black

b> yellow

c> Blue

(16) carbon dioxide.

(17) Carbon Monoxide

(18) CNG, LPG

(19) Low ignition temperatures substance are : potassium and phosphorus.

high ignition temperatures substance are : Coal and charcoal.

(20) (a) ignition temperature (b) air (c) water (d) kerosene (e) calorific value (f) flames (g) pollution.

Short Answer Type Questions Answers

(21)  A material which is burnt to produce heat is called a fuel.

The two common fuels are : Wood, Lpg.

Four characteristics of an Ideal are :

  • It has a high calorific value.
  • It burns easily in air at a moderate rate.
  • It has a proper ignition temperature
  • It is cheap, readily available, and easy to transport.

(22) The amount of heat produced by the complete burning of  A 1 Kilogram of a  fuel is called its calorific value.

It means that calorific value of LPG is 55000 kJ/kg , that if 1 kilogram of LPG is burnt completely , then it will produce 55000 kilojoules of energy.

(23) No, we cant burn a piece of wood by bringing a lighted matchstick because a splinter of wood has a low ignition temperature  but a piece of wood has a high ignition temperature which can not be reached by the small heat produced by a matchstick.

(24) Coal and wood has a high ignition temperature so we need to use paper or kerosene oil to start fire.

(26) The combustion reaction in which a large amount of heat and light are produced in a short time is called rapid combustion.

The immediate burning of cooking gas in a gas stove to give heat and light, is an example of rapid combustion.

(26) The combustion reaction which occurus on its own is called spontaneous combustion.

The burning of white phosphorus on its own room temperature is an example of spontaneous combustion.

(27)  A very fast combustion reaction in which a large amount of heat, light, and sound are produced is called explosive combustion.

The firecrackers which we explode during festival work is an example of explosive combustion.

(28) A combustion cannot be start up without oxygen and in our atmosphere, oxygen is mixed up with air, so air is necessary for combustion.

(29) yes, the process of rusting be called combustion.

Rusting of iron is an exothermic process as heat is released during rusting. Hence, it is a kind of slow combustion. So the process of rusting be called combustion.

(30) we know that Water is heavier that oil. So when it is poured on oil fire, it sinks to the bottom where it evaporates due to heat of fire and thus expands rapidly due to which it may push and splatter fire in all directions.

(31) We all know that water is good conductor of electricity. If water is pouredon an electrical fire, the water could conduct electricity causing the person trying to extinguish the fire to experience an electric shock.

(32) With the help of carbon dioxide extinguisher, we can extinguished the fire produced by burning oil.

(33) When a fire caused by electricity, we must should need to cut electric supply or we need to use blanket to stop giving oxygen to flame.

(34) The simplest way to put of this fire is use to a carbon dioxide fire extinguisher.

(35) If a fire breaks out in our home or neighbour, the first thing we need to do the call the fire service.

(36)  (a) Fire brigade man throws a strong stream of water on a building to get cooled  the burning materials.

(b) we should use water or carbon dioxide if a fire caused by burning wood or papar.

(37)  coal fire consumed a lot of oxygen during burn. If we sleep into a room having close window and doors, then the oxygen supply will be stop and the remaining oxygen on that room will be finished for burning coal. If the oxygen finished, the people on that room will be die.

(38)  (a) A flame is a region where combustion of gaseous substances takes place.

(b) Candle burns with a flame but coal does not burns with a flame. coal is a carbon product and its burning is harmful for environment, but candle is made from wax its burning is not as much harmful as burning of coal .

(39) The reason water extinguishes flames is because it is exceptionally good at absorbing heat.

(40)  CO2 is able to control fires because CO2 being heavier than oxygen and it reduce oxygen supply to the flame.

(41)  We will use a fire blanket or CO2 extinguisher to extinguish the fire.

(42) The examples are :

  • Solid fuels : Coal, wood
  • Liquid fuels : Petrol, Kerosene
  • Gaseous fuels : LPG, CNG

(43) The three zones  of a candles are

  • Innermost zone
  • Middle zone
  • Outer zone

The coldest zone of a candle flame is innermost zone.

(44) Goldsmith blow air with a blow-pipe for melting and moulding the pieces of gold and silver into desired shape to make jewellery.

(45) a> middle zone,  b> outer zone

(46) When CNG burns, it produced very small amount of harmful product and also without producing smoke. That’s how CNG as a fuel in automobile has reduced air pollution in our cities.

(47) The disadvantages of burning wood as a fuel are :

  • The burning of wood produced a lot of smoke which is very harmful for human being.

The cutting down of tress to obtain fuel wood leads to deforestation which is very harmful for the environment.

(48)   The following reasons of LPG is a better domestic fuel than wood are :

  • LPG has a much higher calorific value than wood, so it produces much more heat on burning than an equal mass of wood.
  • LPG burns without producing any smoke but burning of wood produced a lot of smoke

(49)   When a burning candle is covered with an inverted gas jar, the candle gets extinguish after some time  because the supply of fresh air to the burning candle is cut off by the gas jar cover.

(50) The green leaves contain a lot of water. This water does not allow the green leaves to get heated to their  ignition temperature easily and makes the burning of green leaves difficult. On the other hand, since dry leaves do not contain water, they get heated to their ignition temperature  easily.

Long Answer Type Questions Answers:

(51) (a) Those Substance which can burn are called combustible substance.

Three combustible substances are :  Paper, Cloth, Cooking gas.

(b ) Those substances which do not burn are called non-combustible substance.

Three non-combustible substances are : Stone, Glass, Cement.

(52) (a) A Chemical process in which a substance reacts with the oxygen to give  heat and light is called combustion

If a magnesium ribbon is  heated, it starts burning . when a magnesium ribbon burns,  it combines with the oxygen of the air.

The conditions are :

  • Presence of a combustible substance.
  • Presence of a supporter of combustion.
  • Heating the combustible substance to its ignition temperature.

(53) (b) The fuel vapours burn partially in the middle zone, this partial burning of fuel I n the middle zone produces carbon particles. Because of this carbon particles, candle emits light.

(54) Global warming is the rise in temperature  of earth’s atmosphere  caused by the excessive amounts of carbon dioxide in the air.

The gas whose Increasing percentage in air is leading to global warming is Carbon dioxide.

The harmful effect caused by global warming are :

  • Rise the temperature of atmosphere
  • Ice in polar region will melt very fast.
  • Rise in the sea level

(55) Burning of coal, petrol, diesel, produces sulphur dioxide and nitrogen oxide            which goes into the air. Sulphur  dioxide and nitrogen oxides produced by the burning of fuels dissolve in rain water and form acids. The rain water containing acids is called acid rain.

Higher Order Thinking Skills (HOTS)


Air is an essential component for combustion. Without air or more specifically oxygen it is impossible to have combustion. In a closed tank full of petrol an electric spark is struck between two electrodes placed near each other. In this case the petrol will not catch fire because of the absence of any air in the closed tank.


For any object to catch fire the object must reach the ignition temperature. When a piece of paper is heated alone the paper reaches the ignition temperature quickly and catches fire. However, when the paper is wrapped in aluminium pipe the heat applied to it is quickly transferred to the aluminium pipe through conduction.  Aluminium is a good conductor of heat unlike paper so it distributes all the heat in its body and the paper does not attain the ignition temperature.  This is the reason why paper wrapped in aluminium does not catch fire when heated.


If we notice the flame of a candle carefully we can see that there is more than one color. The temperatures of the flames are also different depending on the color of the flames. One beaker of water is heated on the middle yellow part of the candle flame and another beaker is heated on the outer-most blue and non-luminous part of the flame. The beaker that is being heated on the outer-most part of the flame will get hotter faster than the other beaker. The reason behind this is the blue part of the flame is has higher temperature than the yellow flames.


X = Sodium Bicarbonate (Sodium Hydrogencarbonate)

When a lot of Sodium Bicarbonate (X) is released over a fire the heat of the fire decomposes it and produces carbon dioxide gas. This carbon dioxide gas covers the fire like a blanket and stops the supply of oxygen to the fire. Due to this the fire gets extinguished.  Another substance that acts as a fire extinguisher is potassium bicarbonate.


There are many types of combustion. The three main types of combustions are Rapid combustion, Spontaneous combustion and Explosive combustion. The burning of white phosphorus and the burning of coal dust in a coal mine is the example of spontaneous combustion. Burning of LPG stove is an example of rapid combustion. Ignition of cracker is the example of explosive combustion

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