Combustion and Flame Part 1: MCQs (Q1–Q25)
🔥 Combustion and Flame – MCQs for Class 8 Science
Part 1: Q1 – Q25
Q1. Which of the following is NOT a combustible substance?
A) Coal
B) Stone
C) Wood
D) LPG
✅ Correct Answer: B) Stone
Explanation:
- A) Coal – ✔ Combustible.
- B) Stone – ✔ Non-combustible, does not burn.
- C) Wood – Combustible.
- D) LPG – Combustible fuel.
Q2. Which is necessary for combustion to take place?
A) Oxygen
B) Nitrogen
C) Hydrogen
D) Carbon dioxide
✅ Correct Answer: A) Oxygen
Explanation:
- A) Oxygen – ✔ Supports burning.
- B) Nitrogen – Inert, does not support burning.
- C) Hydrogen – Fuel, not supporter.
- D) Carbon dioxide – Extinguishes fire.
Q3. Which is the lowest temperature at which a substance catches fire?
A) Ignition temperature
B) Boiling point
C) Melting point
D) Flash point
✅ Correct Answer: A) Ignition temperature
Explanation:
- A) ✔ Ignition temperature is the minimum temperature at which a substance burns.
- B) Boiling point – Not related to burning.
- C) Melting point – Not related to fire.
- D) Flash point – Not NCERT term for this context.
Q4. Which fuel has the highest calorific value?
A) Wood
B) Petrol
C) LPG
D) Biogas
✅ Correct Answer: C) LPG
Explanation:
- A) Wood – Lower calorific value.
- B) Petrol – Higher, but not the highest.
- C) LPG – ✔ Highest among common fuels (around 55 kJ/g).
- D) Biogas – Less than LPG.
Q5. Which gas is produced when a fuel burns completely?
A) CO
B) SO₂
C) CO₂
D) H₂
✅ Correct Answer: C) CO₂
Explanation:
- A) CO – Incomplete combustion.
- B) SO₂ – Only if sulphur is present.
- C) CO₂ – ✔ Complete combustion → carbon dioxide.
- D) H₂ – Not formed.
Q6. Which of these is a clean fuel?
A) Coal
B) Petrol
C) Diesel
D) CNG
✅ Correct Answer: D) CNG
Explanation:
- A, B, C – Produce smoke, pollutants.
- D) CNG – ✔ Burns cleanly, no smoke.
Q7. Which type of flame is obtained in a Bunsen burner when the air hole is closed?
A) Luminous flame
B) Non-luminous flame
C) Blue flame
D) No flame
✅ Correct Answer: A) Luminous flame
Explanation:
- A) ✔ Yellow, luminous, less hot flame.
- B, C – Appear when air hole is open.
- D) No flame – Incorrect.
Q8. Which zone of a candle flame is the hottest?
A) Outermost zone
B) Middle zone
C) Innermost zone
D) Wick
✅ Correct Answer: A) Outermost zone
Explanation:
- A) ✔ Outermost zone – complete combustion, blue, hottest.
- B) Middle zone – Partial combustion.
- C) Innermost zone – Least hot.
- D) Wick – Burns due to melted wax vapours.
Q9. Which of the following is used in fire extinguishers?
A) Oxygen
B) Carbon dioxide
C) Nitrogen dioxide
D) Ammonia
✅ Correct Answer: B) Carbon dioxide
Explanation:
- A) Oxygen – Supports fire.
- B) ✔ CO₂ cuts oxygen supply, extinguishes fire.
- C, D – Not used in extinguishers.
Q10. Which fuel is used in jet aircrafts?
A) Diesel
B) Petrol
C) Kerosene
D) LPG
✅ Correct Answer: C) Kerosene
Explanation:
- A, B, D – Used in vehicles/cooking.
- C) ✔ Aviation fuel is kerosene.
Q11. Which is an example of a fossil fuel?
A) CNG
B) Biogas
C) Hydrogen
D) Ethanol
✅ Correct Answer: A) CNG
Explanation:
- A) ✔ Fossil fuel derived from natural gas.
- B, C, D – Renewable/alternative fuels.
Q12. Which part of the flame has unburnt wax vapours?
A) Innermost zone
B) Middle zone
C) Outermost zone
D) Wick
✅ Correct Answer: A) Innermost zone
Explanation:
- A) ✔ Innermost zone = unburnt vapours, least hot.
- B) Middle – Partial combustion.
- C) Outer – Complete combustion.
- D) Wick – Source of vapours.
Q13. Which type of combustion occurs suddenly with evolution of heat, light and sound?
A) Rapid combustion
B) Spontaneous combustion
C) Explosion
D) Slow combustion
✅ Correct Answer: C) Explosion
Explanation:
- A) Rapid – Steady burning.
- B) Spontaneous – Without external flame.
- C) ✔ Explosion → sudden release of energy.
- D) Slow – Occurs without flame.
Q14. Which is NOT a characteristic of a good fuel?
A) High calorific value
B) Produces less smoke
C) Easily available
D) High ignition temperature
✅ Correct Answer: D) High ignition temperature
Explanation:
- A, B, C – Desired properties.
- D) ✔ Should have low ignition temperature, not high.
Q15. Which device is used to measure calorific value of a fuel?
A) Thermometer
B) Barometer
C) Bomb calorimeter
D) Hygrometer
✅ Correct Answer: C) Bomb calorimeter
Explanation:
- A, B, D – Not used.
- C) ✔ Bomb calorimeter measures energy released.
Q16. Which gas is poisonous and formed during incomplete combustion?
A) Oxygen
B) CO₂
C) Carbon monoxide (CO)
D) SO₂
✅ Correct Answer: C) Carbon monoxide (CO)
Explanation:
- A) Oxygen – Essential, not poisonous.
- B) CO₂ – Not deadly in small amounts.
- C) ✔ CO – poisonous, binds with haemoglobin.
- D) SO₂ – Irritant, not main product.
Q17. The candle flame is brightest at:
A) Innermost zone
B) Middle zone
C) Outermost zone
D) Wick
✅ Correct Answer: B) Middle zone
Explanation:
- A) Innermost – Dark, least hot.
- B) ✔ Middle zone – partial burning, yellow, bright.
- C) Outermost – Blue, less bright.
- D) Wick – Source, not brightest.
Q18. Which of these is NOT a fire prevention method?
A) Removing combustible substances
B) Cutting oxygen supply
C) Reducing temperature
D) Supplying oxygen continuously
✅ Correct Answer: D) Supplying oxygen continuously
Explanation:
- A, B, C – Correct fire prevention methods.
- D) ✔ Oxygen supply → increases fire.
Q19. Which fuel has the lowest calorific value among these?
A) LPG
B) Petrol
C) Wood
D) CNG
✅ Correct Answer: C) Wood
Explanation:
- A, B, D – High calorific values.
- C) ✔ Wood has lowest (~17–20 kJ/g).
Q20. Which type of combustion is burning of LPG in a stove?
A) Rapid combustion
B) Explosion
C) Slow combustion
D) Spontaneous combustion
✅ Correct Answer: A) Rapid combustion
Explanation:
- A) ✔ Gas burns quickly with heat and light.
- B, C, D – Not suitable.
Q21. Which fire extinguisher is best for electrical fires?
A) Water
B) Sand
C) Foam
D) Carbon dioxide
✅ Correct Answer: D) Carbon dioxide
Explanation:
- A) Water – Dangerous, conducts electricity.
- B) Sand – Works but less effective.
- C) Foam – Used for oil fires.
- D) ✔ CO₂ – safe for electrical fires.
Q22. Which of these fuels is renewable?
A) Coal
B) LPG
C) Biogas
D) CNG
✅ Correct Answer: C) Biogas
Explanation:
- A, B, D – Fossil fuels, non-renewable.
- C) ✔ Biogas → produced from biomass, renewable.
Q23. Which part of the flame is blue in colour?
A) Innermost zone
B) Middle zone
C) Outermost zone
D) Wick
✅ Correct Answer: C) Outermost zone
Explanation:
- A) Innermost – Black, unburnt vapours.
- B) Middle – Yellow, bright.
- C) ✔ Outermost zone – blue, complete combustion.
- D) Wick – Not a flame zone.
Q24. Which type of fire cannot be controlled by water?
A) Wood fire
B) Electrical fire
C) Paper fire
D) Cloth fire
✅ Correct Answer: B) Electrical fire
Explanation:
- A, C, D – Water can extinguish.
- B) ✔ Water conducts electricity, dangerous.
Q25. Which fuel is most suitable for domestic use?
A) Coal
B) Wood
C) LPG
D) Kerosene
✅ Correct Answer: C) LPG
Explanation:
- A, B, D – Produce smoke/pollution.
- C) ✔ LPG is clean, efficient, safe for homes.
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