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Question 1

What is combustion?

A chemical process in which a substance reacts with oxygen to give off heat and light is called combustion.


Question 2

Define combustible substance.

The substance that can reacts with oxygen and gives off heat and light i.e., undergo combustion, is called combustible substances.


Question 3

With the help of given table, mark the combustible and non-combustible substances of your daily life

Material Combustible / non-combustible
Wood Combustible
Paper Combustible
Iron nails Non - Combustible
Kerosene oil Combustible
Stone piece Non – Combustible
Straw Combustible
Charcoal Combustible
Match sticks Combustible
glass Non - Combustible

Question 4

Why we wrapped a blanket around a person who caught fire?

We wrapped a blanket around a person who caught fire, because the fire stops getting the oxygen in required amount for combustion and it extinguishes.

Question 5

What is meant by ignition temperature?

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


Question 6

With the help of an experiment, show that oxygen (air) is necessary for the burning of a candle.

To show the experiment we have to fix three lighted candle on a table, and put a glass chimney over it.

fig a

fig b

fig c

The chimney (fig a) rested on a wooden block in such a way that air can enter the chimney – the candle will continue burning, because it is getting air from the wooden block

The chimney (fig b) rested on the table with no way for air- the candle flickers and gives smoke

The chimney (fig c) rested on table and covered from top with glass plate – the candles goes off as the air is not available.

Question 7

What do you meant by inflammable substances?


The substance which have very low ignition temperature and can easily catch fire with a flame are called inflammable substances.


Question 8

What is rapid combustion?

A combustion that takes place at a high speed is known as rapid combustion.


Question 9

What is spontaneous burning?

In a heap of several substances, when they catches fire, they undergo slow oxidation with evolution of heat. At certain stage when the temperature becomes more than the ignition temperature of any one of the constituent – all of a sudden, it starts burning. This is called spontaneous burning.


Question 10

Define the term ‘explosion’.

A process of combustion in which a large amount of gases are evolved with the production of tremendous amount of heat, light and sound is called explosion.


Question 11

Charcoal does not burn with flame but glows only.

Charcoal does not burn with flame because it is not volatile in nature or does not vapourise on burning, so its glows only.


Question 12

What is meant by the term ‘fuel’?

A fuel is a substance, which may be burnt to produce considerable heat without the formation of objectionable products.


Question 13

Describe the various zones of a flame.

A flame has four zones in it

a. the outermost thin transparent faint bluish non- luminous region of complete combustion. It is the hottest zone of the flame.

b. the middle bright luminous zone of partial combustion.

c. the innermost, coldest dark zone, consist of hot vapour and called as zone of no combustion.

d. blue zone near the bottom of the flame is due to burning of CO. CO is formed due to incomplete combustion.

Different zones of a candle flame

Question 14

Why water is not used to check the fire by electric short circuit?


Water is not used at all to check the fire by electric short circuit because it is a good conductor of electricity and may result in electrocution or electric shock.


Question 15

What are the constituents of a foam type fire extinguisher?

The foam type extinguisher is also called as ‘soda acid’ fire extinguisher. The constituents are:
  • a. dilute sulphuric acid
  • b. sodium bicarbonate (soda)
  • when it is operated it comes out under pressure in the form of a foam, which covers the surface of fire and controls it.

    Question 16

    Why do the goldsmith use the outermost zone of the burning flame?


    Goldsmith blow the outermost zone of a flame with a metallic blow pipe for melting gold and silver because this is the hottest part of the flame.


    Question 17

    What is meant by ‘deforestation’?

    Cutting of trees is called as deforestation.


    Question 18

    What are the different harmful products of burning of a fuel?

    The harmful products that form during the fuel combustion are:

    a. wood, charcoal and petroleum – when used as fuel, it release unburnt carbon particles, which are dangerous pollutant causing respiratory disorders

    b. incomplete combustion form carbon monoxide gas – a poisonous gas, that can even kill a person if coal is burnt in a closed room and person is sleeping in that room.

    Question 19

    Explain the term’ global warming’.


    The combustion of fuels release carbondioxide in the environment. When the percentage of carbondioxide increases in the air and makes the earth surface hot – it is believed to cause global warming.


    Question 20

    What is acid rain?

    The gases like nitrogen oxide, sulphur dioxide etc. present in the atmosphere as pollutants when these gases dissolve in rain water and form acids and reaches to the earth as rain called as acid rain.


    Question 21

    Why CNG is preferable for vehicles in respect to petrol and diesel?

    CNG (compressed natural gas) in preferable for vehicles in respect to petrol and diesel, because
    a. it leaves least residues

    b. it is cheaper

    c. it is eco-friendly.


    Question 22

    Why any of the fuel is not considered as an ideal fuel?

    The fuel is not considered as an ideal fuel because all the fuels are differ in their cost and efficiency i.e., its calorific value.

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