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NCERT Solutions for Class 8th Science


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Chapter 6. Combustion And Flame

Additional Questions With Solutions




Combustion And Flame

Ques: What is combustion?

Ans: The chemical process in which a substance reacts with oxygen and gives heat is called combustion.

Ques: What is fuel?

Ans: The substance that undergoes combustion is said to be combustible. It is also called a fuel.

Ques: Name the reaction by which heat and light are produced in the sun.

Ans: Nuclear reaction.

Ques: What is ignition temperature?

Ans: The lowest temperature at which a substance catches fire is called its ignition temperature.

Ques: Why does the paper cup not burn while boiling water?

Ans: The heat supplied to the paper cup is transferred to water by conduction. So, in the presence of water, the ignition temperature of paper is not reached. Hence, it does not burn.

Ques: Write three essential requirements for producing fire.


 (i) Inflammable substance - fuels.

 (ii) Ignition temperature

(iii) Oxygen

Ques: Which extinguisher is used to control the fire involving electric equipment and inflammable material like petrol?

Ans: CO2

Ques: How can fire be controlled suddenly?

Ans: The contact between fuel and oxygen is cut off to control the fire. For this, there  are many processes like watering, use of CO2 . It also brings down the ignition temperature.

Ques: What is the advantages of use CO2 to control the fire.

Ans: CO2 does not harm the electric equipment while watering causes electric conduction.

Ques: Explain how CO2 is able to control fires?

Ans: CO2  being heavier than oxygen, covers the fire like blanket. Since the contact between the fuel and oxygen is cut off, the fire is controlled.

Ques: Write the types of combustion.

Ans: There are three types of combustion

(i) Rapid combustion

(ii) Spontaneous combustion.

(iii) Explosion.

Ques: The candle gives flame during burning but charcoal does do so. Why?
Ans: The substances which vaporize during burning, gives flames. The candle is vaporised but the charcoal is not vaporised.  

Ques: What are the various zone of flame?

Ans: The various zone of flame:

(i)   Dark zone

(ii)  Luminous zone

(iii) Non – luminous zone

Ques: Which zone of a flame does a goldsmith use for melting gold and silver and why?

Ans: The goldsmith uses dark zone. Since it is the hottest part of flame.

Ques: What do you mean by calorif value? Write its units.

Ans: The amount of heat energy produced on complete combustion of 1 kg of a fuel is called its calorific value. Its unit is kilojoules per kg (kj/kg)

Ques: What is the main cause of global warming?

Ans: CO2

Ques:Which poisonous gas are given by incomplete combustion of fuels?

 Ans: Carbon monoxide.  


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