Combustion and Flame MCQs Class 8
Combustion and Flame MCQs Class 8
Class: CBSE Class 8
Subject: Science
Section: Section 6 – Combustion and Flame
Topic: Combustion and Flame MCQs
Board: CBSE Board Examinations
Subject: Science
Section: Section 6 – Combustion and Flame
Topic: Combustion and Flame MCQs
Board: CBSE Board Examinations
1. The process of burning of a substance in air is called:
Answer: b) Combustion
Combustion is a chemical process in which a substance reacts rapidly with oxygen producing heat and usually light. Burning of fuels like wood, coal and LPG are common examples.
Combustion is a chemical process in which a substance reacts rapidly with oxygen producing heat and usually light. Burning of fuels like wood, coal and LPG are common examples.
2. Which of the following is not a combustible substance?
Answer: c) Sand
Combustible substances burn in air producing heat and light. Sand does not burn, hence it is a non‑combustible substance.
Combustible substances burn in air producing heat and light. Sand does not burn, hence it is a non‑combustible substance.
3. The lowest temperature at which a substance catches fire is called:
Answer: c) Ignition temperature
Ignition temperature is the minimum temperature required for a substance to start burning. Fuels with low ignition temperature catch fire easily.
Ignition temperature is the minimum temperature required for a substance to start burning. Fuels with low ignition temperature catch fire easily.
4. Which gas is essential for combustion?
Answer: b) Oxygen
Oxygen supports burning. Without oxygen, combustion cannot take place. That is why fire extinguishers cut off oxygen supply.
Oxygen supports burning. Without oxygen, combustion cannot take place. That is why fire extinguishers cut off oxygen supply.
5. A substance that burns to produce heat energy is called:
Answer: a) Fuel
Fuels like coal, LPG, petrol and wood burn to release useful heat energy used for cooking, transport and industries.
Fuels like coal, LPG, petrol and wood burn to release useful heat energy used for cooking, transport and industries.
6. Which of the following is a liquid fuel?
Answer: b) Petrol
Petrol is a liquid fossil fuel widely used in automobiles due to its high calorific value and easy combustion.
Petrol is a liquid fossil fuel widely used in automobiles due to its high calorific value and easy combustion.
7. The heat produced by complete burning of 1 kg fuel is called:
Answer: b) Calorific value
Calorific value measures the energy content of a fuel. Higher calorific value means more heat energy on burning.
Calorific value measures the energy content of a fuel. Higher calorific value means more heat energy on burning.
8. The unit of calorific value is:
Answer: b) kJ/kg
Calorific value is expressed in kilojoule per kilogram indicating heat energy released by 1 kg of fuel.
Calorific value is expressed in kilojoule per kilogram indicating heat energy released by 1 kg of fuel.
9. Which fuel is known as a clean fuel?
Answer: c) LPG
LPG burns completely without producing smoke or harmful gases, making it a clean domestic fuel.
LPG burns completely without producing smoke or harmful gases, making it a clean domestic fuel.
10. The non‑luminous zone of a flame is the:
Answer: c) Blue zone
The blue zone is the hottest part where complete combustion occurs producing maximum heat and very little light.
The blue zone is the hottest part where complete combustion occurs producing maximum heat and very little light.
11. Which zone of a candle flame is the hottest?
Answer: a) Outer zone
The outer zone has complete combustion and highest temperature, hence it is the hottest part of the flame.
The outer zone has complete combustion and highest temperature, hence it is the hottest part of the flame.
12. Incomplete combustion produces:
Answer: b) Carbon monoxide
Incomplete combustion forms carbon monoxide, a poisonous gas that can cause suffocation and death.
Incomplete combustion forms carbon monoxide, a poisonous gas that can cause suffocation and death.
13. Fire can be controlled by:
Answer: d) All of these
Fire needs fuel, oxygen and heat. Removing any one stops combustion. Fire extinguishers work on this principle.
Fire needs fuel, oxygen and heat. Removing any one stops combustion. Fire extinguishers work on this principle.
14. Water is not suitable for extinguishing oil fires because:
Answer: a) Oil floats on water
Oil floats and spreads over water, causing fire to spread instead of stopping.
Oil floats and spreads over water, causing fire to spread instead of stopping.
15. Which extinguisher is used for electrical fires?
Answer: c) CO₂ extinguisher
CO₂ cuts off oxygen supply without conducting electricity, making it safe for electrical fires.
CO₂ cuts off oxygen supply without conducting electricity, making it safe for electrical fires.
16. Burning of magnesium ribbon is an example of:
Answer: b) Rapid combustion
Magnesium burns quickly with bright white flame producing heat and light rapidly.
Magnesium burns quickly with bright white flame producing heat and light rapidly.
17. Spontaneous combustion occurs when:
Answer: b) Substance catches fire on its own
In spontaneous combustion, materials like phosphorus catch fire without external flame due to low ignition temperature.
In spontaneous combustion, materials like phosphorus catch fire without external flame due to low ignition temperature.
18. Explosion is a type of combustion in which:
Answer: c) Large amount of gas and heat release suddenly
Explosions produce heat, light, sound and gases instantly, like firecrackers.
Explosions produce heat, light, sound and gases instantly, like firecrackers.
19. Which fuel has the highest calorific value?
Answer: c) Hydrogen
Hydrogen has very high calorific value and burns to form water, making it an efficient future fuel.
Hydrogen has very high calorific value and burns to form water, making it an efficient future fuel.
20. The substance used in fire extinguishers to cut oxygen supply is:
Answer: b) Carbon dioxide
Carbon dioxide is heavier than air and forms a blanket over fire, cutting oxygen supply and extinguishing flames.
Carbon dioxide is heavier than air and forms a blanket over fire, cutting oxygen supply and extinguishing flames.