Page 77 - Science Class 08

i When combustion starts without igniting, the combustible substance is called spontaneous
combustion.
i When a substance starts burning as soon as it is ignited and produces a large amount of heat
and light, is called rapid combustion.

i In slow combustion, no ignition or external heat is required.
i Water should not be used to put out the fire which is caused by electric current.
i The effects of burning of fuels on environment include pollution, global warming and acid rain.

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Exercise
A. Tick (3) the correct op on.
1. Which of the following is not a combus ble substance?
(a) Wood (b) Clothes
(c) Iron (d) Coke

2. Which of the following supports burning?
(a) Oxygen (b) Hydrogen
(c) Nitrogen (d) Ozone
3. Burning of a ribbon of phosphorus is an example of:

(a) Rapid combus on (b) Spontaneous combus on
(c) Slow combus on (d) Both (a) & (c)
4. What type of fire ex nguisher is used to put out the fire caused by oil?

(a) Water (b) Soda-acid
(c) Foam (d) None of these
5. Which of the following zones of the flame shows no combus on?
(a) Non-luminous zone (b) Luminous zone

(c) Central zone (d) Innermost zone
B. Fill in the blanks.
1. During incomplete combus on, methane releases ____________________ , water and
energy.
2. Igni on temperature of different combus ble substances is ____________________ .
3. Combus on of LPG is an example of ____________________ combus on.
4. Highly ____________________ substances should not be kept in hot places or near
unprotected flames.
5. Since carbon tetrachloride vapours are ____________________ than air, they se le down
on the burning material and cut of the air supply.
C. Write True or False.

1. All the combus ble substances contain carbon.
2. Most of the fuels are made of hydrocarbons.
3. Petrol has higher igni on temperature than coal.

Science-8 77