50 Very Short Answer Type Questions & Answers

1. Q1. What is combustion?
   A chemical reaction of a substance with oxygen producing heat and often light.
2. Q2. What is a fuel?
   A substance that burns to produce heat (e.g., wood, petrol).
3. Q3. Define ignition temperature.
   The minimum temperature required to start combustion.
4. Q4. What is an oxidiser?
   A substance that provides oxygen to support combustion.
5. Q5. Give an example of complete combustion.
   Burning methane: CH₄ + 2O₂ → CO₂ + 2H₂O + heat.
6. Q6. What is incomplete combustion?
   Combustion with limited oxygen producing CO, soot and less heat.
7. Q7. Name a dangerous product of incomplete combustion.
   Carbon monoxide (CO).
8. Q8. What are the three zones of a candle flame?
   Inner (dark) zone, middle (luminous) zone, outer (non-luminous) zone.
9. Q9. Which zone of flame is the hottest?
   The outer (non-luminous) zone.
10. Q10. Why is the middle zone luminous?
    Due to glowing carbon particles from incomplete combustion.
11. Q11. What is smouldering combustion?
    Slow, flameless combustion (e.g., glowing coal).
12. Q12. Give an example of spontaneous combustion.
    Oily rags catching fire due to self-heating.
13. Q13. What is explosive combustion?
    Very rapid combustion producing large heat and gases in a short time.
14. Q14. State the fire triangle.
    Heat, fuel and oxygen.
15. Q15. How can fire be extinguished by removing heat?
    By cooling with water to lower temperature below ignition point.
16. Q16. How does CO₂ extinguisher work?
    It displaces oxygen, suffocating the fire.
17. Q17. Which extinguisher is unsuitable for electrical fires?
    Water extinguisher (conducts electricity).
18. Q18. Define inflammable and combustible.
    Both mean easily set on fire; 'inflammable' and 'combustible' are similar.
19. Q19. What causes soot formation?
    Incomplete combustion producing carbon particles (soot).
20. Q20. Why is ventilation important while burning fuel indoors?
    To provide oxygen and prevent buildup of poisonous gases like CO.
21. Q21. What is meant by flameless combustion?
    Combustion occurring without visible flame, e.g., smouldering coal.
22. Q22. Name one use of combustion in daily life.
    Cooking on gas stove.
23. Q23. What is meant by heat of combustion?
    The heat released when a substance completely burns in oxygen.
24. Q24. Why does a Bunsen burner flame turn blue?
    Because of complete combustion with sufficient air supply.
25. Q25. What is meant by 'ignition'?
    The act of starting combustion by supplying heat.
26. Q26. Give one way to prevent fire in kitchen.
    Keep flammable items away from stove and ensure proper ventilation.
27. Q27. What gas is produced in complete combustion of hydrocarbons?
    Carbon dioxide (CO₂) and water vapour.
28. Q28. How does foam extinguisher work on oil fires?
    It forms a blanket over fuel, cutting off oxygen supply.
29. Q29. What is the role of the wick in a candle?
    It draws up molten wax to feed fuel vapour to the flame.
30. Q30. Why should oily rags be stored safely?
    To prevent spontaneous combustion due to self-heating.
31. Q31. What is a fuel-air mixture?
    A mixture of fuel vapour and air that can burn (e.g., petrol-air in engines).
32. Q32. Name a sign of incomplete combustion in a stove.
    Yellow flame and soot deposits.
33. Q33. What is the simplest test for CO₂?
    Passing gas through lime water; it turns milky.
34. Q34. Why is CO called dangerous?
    It is colourless, odourless and poisonous, binds with haemoglobin.
35. Q35. What change occurs when a matchstick is struck?
    Friction produces heat raising match head to ignition temperature, starting combustion.
36. Q36. What is the product when carbon burns in excess oxygen?
    Carbon dioxide (CO₂).
37. Q37. Give an example of combustion used in industry.
    Smelting in metallurgy using furnace heat.
38. Q38. What is meant by a 'flash point' (simple idea)?
    Lowest temperature at which vapour above a liquid ignites briefly.
39. Q39. How does increasing air supply affect flame?
    Promotes complete combustion and may make flame bluer and hotter.
40. Q40. What safety step to take for electrical fires?
    Use CO₂ or dry powder extinguisher; switch off electricity if safe.
41. Q41. What is meant by 'combustible material'?
    A material that can catch fire and burn easily.
42. Q42. State one difference between combustion and corrosion (short).
    Combustion is rapid with heat and light; corrosion is slow deterioration by oxidation.
43. Q43. Why does a candle flame have a dark inner core?
    Because unburnt vapour and gases are present and combustion is incomplete there.
44. Q44. Name a fire extinguisher suitable for kitchen oil fires.
    Foam extinguisher or dry powder extinguisher (small fires).
45. Q45. What is meant by 'fuel efficiency' in engines (brief)?
    How effectively fuel's energy is converted into useful work.
46. Q46. Why should chimneys be cleaned regularly?
    To remove soot and ensure proper ventilation and safe combustion.
47. Q47. How can you reduce incomplete combustion at home?
    Provide sufficient air, maintain burners and ensure clean fuel supply.
48. Q48. What happens when hydrogen burns in air?
    It forms water vapour (2H₂ + O₂ → 2H₂O) releasing heat.
49. Q49. What is the cause of chimney fires?
    Accumulation of combustible soot and tar that catches fire.
50. Q50. Give a short safety rule about matches.
    Strike matches away from the body and extinguish properly; keep out of children\'s reach.

These questions and answers follow the NCERT syllabus closely and are ideal for quick revision before tests and board exams.