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Vidaara.orgClass 8 · Mathematics
CodeVID-M8-WS
Combustion and Flame — Practice Worksheet
Chapter: Combustion and Flame
Topic: Combustion and Flame
Maximum Marks: 27
Time: 30 minutes
Name: ____________________ Roll No.: __________ Date: ____________

General Instructions

  • All questions are compulsory.
  • Choose the correct option (A, B, C or D) for each question.
  • The answer key is at the end — try the paper first!
Section A — Multiple Choice (1 mark each) 15 × 1 = 15 marks
1.
Combustion is the burning of a substance in:
  • A.Nitrogen
  • B.Oxygen
  • C.Water
  • D.Carbon dioxide
2.
Which of these is a combustible substance?
  • A.Glass
  • B.Stone
  • C.Wood
  • D.Iron rod
3.
The three conditions for combustion are fuel, ignition temperature and:
  • A.A supporter of combustion (oxygen)
  • B.Water
  • C.Sound
  • D.Light only
4.
The lowest temperature at which a substance catches fire is its:
  • A.Boiling point
  • B.Calorific value
  • C.Ignition temperature
  • D.Melting point
5.
Substances with a very low ignition temperature that catch fire easily are:
  • A.Non-combustible
  • B.Inflammable
  • C.Metals
  • D.Supporters of combustion
6.
Burning of LPG when a stove is lit is an example of ___ combustion.
  • A.Spontaneous
  • B.Rapid
  • C.Slow
  • D.Explosion
7.
A substance bursting into flames on its own without a flame being brought near is ___ combustion.
  • A.Rapid
  • B.Spontaneous
  • C.Explosion
  • D.Incomplete
8.
The sudden reaction releasing heat, light, sound and gas, like a firecracker bursting, is an:
  • A.Explosion
  • B.Rapid combustion
  • C.Spontaneous combustion
  • D.Slow burning
9.
A flame is produced only when the burning substance gives off:
  • A.Vapours (gases)
  • B.Water
  • C.Ash only
  • D.Sound
10.
Which zone of a candle flame is the LEAST hot?
  • A.Dark innermost zone
  • B.Yellow middle zone
  • C.Blue outer zone
  • D.All are equally hot
11.
Goldsmiths heat metals with the outer part of a flame because it is the:
  • A.Coldest part
  • B.Hottest part
  • C.Darkest part
  • D.Yellow part
12.
The amount of heat produced on completely burning 1 kg of a fuel is its:
  • A.Ignition temperature
  • B.Calorific value
  • C.Boiling point
  • D.Density
13.
Incomplete combustion of fuels can produce the poisonous gas:
  • A.Oxygen
  • B.Carbon monoxide
  • C.Nitrogen
  • D.Hydrogen
14.
Water should NOT be used to put out fires caused by:
  • A.Paper
  • B.Wood
  • C.Electrical equipment or oil
  • D.Dry leaves
15.
A carbon dioxide extinguisher puts out a fire by:
  • A.Adding more oxygen
  • B.Cutting off the oxygen supply
  • C.Adding fuel
  • D.Raising the temperature
Section B — Challenge / Olympiad (2 marks each) 6 × 2 = 12 marks
16.
Sand is thrown on a small fire to put it out because the sand:
  • A.Cuts off the air (oxygen) supply
  • B.Adds fuel
  • C.Raises the temperature
  • D.Adds oxygen
17.
A matchstick lights at once but a coal piece needs much heating. This is because they have different:
  • A.Ignition temperatures
  • B.Colours
  • C.Weights only
  • D.Smells
18.
Why is a stove flame adjusted to burn blue rather than yellow for cooking?
  • A.A blue flame means complete combustion and more heat with less soot
  • B.A blue flame is colder
  • C.A yellow flame is hotter
  • D.A blue flame uses no fuel
19.
CO2 is a good fire extinguisher for electrical fires mainly because it:
  • A.Does not conduct electricity and cuts off oxygen
  • B.Adds oxygen
  • C.Is a fuel
  • D.Conducts electricity well
20.
Of two fuels, one leaves a lot of ash and smoke while the other burns cleanly with a high calorific value. The better fuel is the one that:
  • A.Burns cleanly with high calorific value
  • B.Leaves more ash
  • C.Produces more smoke
  • D.Gives less heat
21.
Burning fossil fuels releases carbon dioxide, which contributes to:
  • A.Global warming
  • B.Cooling the Earth
  • C.Cleaner air
  • D.Making fuels renewable

Answer Key

Section A — Multiple Choice (1 mark each)
  1. (B) Oxygen
  2. (C) Wood
  3. (A) A supporter of combustion (oxygen)
  4. (C) Ignition temperature
  5. (B) Inflammable
  6. (B) Rapid
  7. (B) Spontaneous
  8. (A) Explosion
  9. (A) Vapours (gases)
  10. (A) Dark innermost zone
  11. (B) Hottest part
  12. (B) Calorific value
  13. (B) Carbon monoxide
  14. (C) Electrical equipment or oil
  15. (B) Cutting off the oxygen supply
Section B — Challenge / Olympiad (2 marks each)
  1. (A) Cuts off the air (oxygen) supply
  2. (A) Ignition temperatures
  3. (A) A blue flame means complete combustion and more heat with less soot
  4. (A) Does not conduct electricity and cuts off oxygen
  5. (A) Burns cleanly with high calorific value
  6. (A) Global warming
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