CBSE – 8th Standard Science

CBSE - 8th Standard Science

Question Bank – Chapter 6 – Combustion and Flame

Chapter 6 



Q1. List conditions under which combustion can take place.

Ans. In the Presence of oxygen, heat and fuel a combustion can take.


Q2. How the use of CNG in automobiles has reduced pollution in our cities?

Ans. CNG is a cleaner fuel, it produces the harmful products in very small amounts

While use of diesel and petrol as fuels in automobiles causes air pollution .


Q.3  What is the most common fire extinguisher?

Ans. Water is mostly used to extinguish fire, it cools the combustible material so that its temperature is brought below its ignition temperature, water  vapours also surround the combustible material, helping in cutting off the supply of air.


Q.4  Why CO2 is used to control fires involving electrical equipment?

Ans. For fires involving electrical equipment carbon dioxide (CO2) is the best extinguisher it covers the fire like a blanket to cut off  contact between the fuel and oxygen, and fire is controlled also it does not harm the electrical equipment


Q.5  LPG is a better domestic fuel than wood.

Ans. LPG is cheaper, harmless fuel with high caloric value but  burning of wood gives a lot of smoke which is very harmful for human beings. It causes respiratory problem and deforestation which is quite harmful to the environment.


Q.6  What is Spontaneous combustion?

Ans. The type of combustion in which a material suddenly bursts into flames, without the application of any apparent cause is called spontaneous combustion


Q.7  Name the different zones of Flame?

Ans. There are three different zones of a flame – dark zone, luminous zone and non-luminous zone.

  1. 8 What is an Ideal Fuel?

Ans. An ideal fuel is cheap, readily available, readily combustible and easy to transport with high calorific value. It does not produce gases or residues that pollute the environment.


Q.9  Paper by itself catches fire easily whereas a piece of paper wrapped around an  aluminium  pipe does not.

Ans. A combustible substance cannot catch fire or burn as long as its temperature is lower than its ignition temperature, paper is highly inflamable but pipe is not.


Q.10  Name the unit in which the calorific value of a fuel is expressed.

Ans. The calorific value of a fuel is expressed in a unit called  kilojoule per kg (kJ/kg).


Q.11 Explain how CO2 is able to control fires.

Ans.  CO2, being heavier than oxygen, covers the fire like a blanket. Since the contact between the fuel and oxygen is cut off, the fire is controlled. The added advantage of CO2 is that in most cases it is harmless.



Q.12  It is difficult to burn a heap of green leaves but dry leaves catch fire easily. Explain.

Ans. The ignition temperature of dry leaves is very small so they burn easily, while green leaves have water inside they don’t catch fire easily.


Q.13   Which zone of a flame does a goldsmith use for melting gold and silver and why?

Ans. Goldsmiths blow the outermost zone of a flame with a metallic blow-pipe for melting gold and silver as this is the hottest part of flame.


Q.14  What are harmful effects of Global warming?

Ans. Global warming is the rise in temperature of the atmosphere of the earth. This results, sun burn and melting of polar glaciers, which  leads to a rise in the sea level, causing floods in the coastal areas.


Q.15  What are mostly used fuels?

Ans. LPG ,cow dung, wood, coal, charcoal, petrol, diesel, compressed natural gas (CNG),are mostly used Fuels .





  1. How will you distinguish between fire extinguishing action of water and CO2 ?

      2.Define fuel efficiency?

  1. If you find such a symbol/sign on a box etc, what does it represent?