Combustion and Flame – Short Answer Type Questions

CBSE Class 8 Science | Chapter 6: Combustion and Flame — 50 Short Answer Q&A (Topic-wise)

CBSE Class 8 Science — Chapter 6: Combustion and Flame

50 Short Answer Questions — Topic-wise • NCERT-aligned • Board-exam standard

Class: 8

Subject: Science

Chapter: Combustion & Flame

CBSE Board Examinations (Study order):

Q1. What is combustion?
A chemical reaction of a substance with oxygen producing heat and often light.
Q2. What is a fuel?
A substance that burns to release heat (solid, liquid or gas).
Q3. Define oxidiser.
A substance that provides oxygen or accepts electrons to support combustion.
Q4. What is ignition temperature?
The minimum temperature at which a substance catches fire.
Q5. What is meant by 'ignition'?
The act of starting combustion by supplying sufficient heat.
Q6. Give one everyday example of combustion.
Burning of a candle or wood in a stove.
Q7. What does flame indicate?
Presence of gaseous combustion producing visible light and heat.
Q8. Name the products of complete combustion of a hydrocarbon.
Carbon dioxide (CO₂) and water vapour (H₂O).

Q9. What is rapid combustion?
Combustion that occurs quickly with evolution of heat and light (e.g., wood burning).
Q10. Define explosive combustion.
Extremely rapid combustion releasing large amounts of energy and gases suddenly.
Q11. What is smouldering combustion?
Slow, flameless burning of solid fuels (e.g., glowing charcoal).
Q12. What is spontaneous combustion?
When a material catches fire without external flame due to self-heating.
Q13. Give an example of spontaneous combustion.
Oily rags left in a pile catching fire.
Q14. What is flameless combustion?
Combustion taking place without visible flame, similar to smouldering.
Q15. Which combustion type is used in explosives?
Explosive combustion.
Q16. Which type is common in coal underground fires?
Smouldering (flameless) combustion.

Q17. Name the three zones of a candle flame.
Inner (dark), middle (luminous) and outer (non-luminous) zones.
Q18. Describe the inner zone briefly.
Dark region with unburnt vapours; combustion is incomplete and temperature is lowest.
Q19. Describe the middle zone briefly.
Luminous yellow region with glowing carbon particles due to partial combustion.
Q20. Describe the outer zone briefly.
Outer non-luminous blue region where complete combustion occurs and is hottest.
Q21. Why does the middle zone appear yellow?
Because tiny carbon particles glow and emit yellow light.
Q22. Which zone has the highest temperature?
The outer non-luminous zone.
Q23. What should students draw about flame for exams?
A labeled diagram of candle flame showing three zones and short descriptions.
Q24. What feeds the flame in a candle?
Wax melts and is drawn up by the wick as vapour which burns.

Q25. Define complete combustion.
Burning in plenty of oxygen producing CO₂ and H₂O only.
Q26. Define incomplete combustion.
Burning with limited oxygen producing CO, soot and less heat.
Q27. Write balanced equation for complete combustion of methane.
CH₄ + 2O₂ → CO₂ + 2H₂O + heat.
Q28. Name two products of incomplete combustion.
Carbon monoxide (CO) and soot (carbon particles).
Q29. Why is CO dangerous?
It is colourless, odourless and binds to haemoglobin, causing poisoning.
Q30. How to detect CO₂ in experiments?
Pass gas through lime water; it turns milky (white precipitate forms).
Q31. Suggest one measure to reduce incomplete combustion in stoves.
Ensure proper air supply and maintain burners cleanly.
Q32. What causes yellow flame in stoves?
Insufficient air leading to incomplete combustion and soot formation.
Q33. Explain why complete combustion gives more heat.
Because fuel oxidises fully releasing maximum chemical energy.

Q34. What is the fire triangle?
Three essentials for fire: heat, fuel and oxygen.
Q35. How does water extinguish fire?
Cools the fire removing heat and may also create steam to reduce oxygen locally.
Q36. How does foam extinguisher work?
Forms a blanket over fuel cutting off oxygen supply.
Q37. When is CO₂ extinguisher used?
For electrical and small oil/chemical fires where water is unsuitable.
Q38. Why not use water on oil fires?
Water can spread oil and worsen the fire due to density and splattering.
Q39. What is a dry powder extinguisher used for?
Versatile use on oil, gas and electrical fires by interrupting chemical reactions.
Q40. Name one preventive step in homes to avoid fires.
Keep flammable materials away from heat sources and store fuels safely.

Q41. Name two everyday applications of combustion.
Cooking on stoves and running internal combustion engines.
Q42. How does combustion contribute to air pollution?
Incomplete combustion emits CO, soot and unburnt hydrocarbons polluting air.
Q43. What is meant by fuel efficiency?
Measure of how effectively fuel's chemical energy is converted into useful work.
Q44. How can combustion be made cleaner?
Use cleaner fuels, ensure complete combustion and install filters or catalytic converters.
Q45. Give one industrial use of combustion.
Generation of heat in furnaces for metal smelting.

Q46. What simple experiment shows CO₂ production?
Burn a candle and pass its exhaust gas through lime water; it turns milky.
Q47. What diagram should be practiced for exams?
Labeled diagram of a candle flame showing three zones and brief notes.
Q48. How to show incomplete combustion using a candle?
Partly cover the flame so oxygen is limited; soot forms on a cool surface placed above it.

Q49. Give two safety rules for handling matches and lighters.
Strike matches away from the body and keep them out of children's reach; switch off lighters after use.
Q50. Why should chimneys and stoves be maintained?
To remove soot buildup, ensure proper ventilation and prevent carbon monoxide risks.

These topic-wise short answer questions and answers are strictly based on NCERT content and ideal for CBSE Class 8 board-exam standard revision.