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class VIII

Key Concepts

acids and bases, calorific value, combustion, deforestation, explosion, flame, fire extinguisher, fuel, fuel efficiency, global warming, ideal fuel, iginition temperature, inflammable substances, fractional column

essential questions

1. What are some of the essential requirements for combustion?
2. Why is it important to maintain a balance between combustion of fuels and environment?


  1. Define combustions.
  2. Define calorific value.
  3. What is ideal fuel?
  4. Define fuel efficiency
  5. Define explosion. How does it happen?
  6. Like fuel the sun also provides heat and light. The process taking place in the sun is called: a) combustion b) nuclear process c) Burning d) all of these
  7. Coal burns with ____ a) flame b) only glow c) both flame and glow d) none of these
  8. Burning of charcoal in a closed room will produce: a) carbon di oxide b) nitrogen dioxide c) carbon monoxide d) all of these
  9. The substances which have very low ignition temperature will a) catch fire easily b) will not catch fire c) catch fire after sometime d) none of these
  10. CNG and LPG are the examples of a) solid fuels b) liquid fuels c) gaseous fuels d) they are not fuels
  11. Ignition temperature is a) lowest temperature at catch fire b) higher temperature at catch fire  c) any temperature  d) none of these
  12. Combustion is a a) chemical process b) physical process c) both of these processes  d) none of these processes
  13. The products of combustion are: a) carbon dioxide and water b) oxygen and water  c) Only carbon di oxide  d) only oxygen
  14. There are following zones of a flame :  a) two   b) three  c) four  d) no zone
  15. Which one of the following has the highest calorific value? a) kerosene b) biogas  c) LPG  d) petrol
  16. The substance expected to have the highest ignition temperature out of the following is:  a) kerosene   b) petrol    c) coal    d) alcohol
  17. The calorific value of a fuel is expressed in a unit called: a) kilojoule per liter  b) kilogram per millilitre     c) kilojoule per gram   d) kilojoule per kilogram
  18. In villages, people use wood as fuel because: a) it is considered to be an ideal fuel     b) of its easy availability and low cost     c) it is environment friendly      d) it catches fire easily
  19. Which among the following is considered as the cleanest fuel? cow dung cake , petrol, kerosene, hydrogen gas. Put them in ascending order.
  20. Which of the following you will choose for extinguishing fire: a) Soda acid extinguisher c) Liquid carbon dioxide extinguisher d) a spray of water
  21. In which zone of a candle, no combustion take place? a) inner   b) middle   c) outer  d) all the three zone
  22. Rusting of Iron is also know as_________ a) galvanization    b) Alloying   c) tinning  d) oxidation


  1. The type of combustion in which heat, light and sound is produced is: a) slow combustion b) spontaneous combustion c) incomplete combustion  d) rapid explosion combustion
  2. Which substance give heat and light after combustion: a) flame b) fuel c) combustion d) none of these
  3. A substance which reacts with oxygen giving heat is called a combustible substance. Which one of the following is a combustible substance: a) iron nail b) glass c) stone piece d) wood
  4. Burning coal in a closed room will produce____ a) carbon dioxide  b) nitrogen oxides c) sulphur dioxie  d) carbon monoxide
  5. Water is used to extinguish fire because it ……………..  a) Lowers the ignition temperature of the burning substance   b) Raises the ignition temperature of the burning substance    c) Cools the burning substance to a temperature below its ignition temperature    d) conducts heat
  6. Magnesium ribbon on burning in air produces : a) magnesium oxide, water and light  b) magnesium oxide and heat  c) magnesium oxide, heat and light  d) magnesium oxide, water and heat
  7. Which of the following is not a combustible substance: a) camphor b) glass c) straw d) alcohol
  8. The substance that does not burn with flame is : a) LPG b) camphor c) dry grass d) charcoal
  9. When air is passed through red hot coke, a gaseous fuel is produced. The name of this gaseous fuel and its composition are respectively:   a) Natural gas, CO+H2    b)Producer gas, N2 +CO    c) Water gas, H2 + CO    d) None of these
  10. Write the difference between: a) Rapid combustion and spontaneous combustion  b) Calorific value and Ideal fuel
  11. Classify the following in two categories: Petrol, diesel, coal, petroleum, air, water, cow dung cakes, sunlight, forests and minerals
Exhaustible Inexhaustible


11. Match the following :  a) Rusting                    i) Explosion

b)Burning of paper     ii) Spontaneous combustion

c) Sodium                     iii) Rapid combustion

d) Fire crackers            iv) Slow combustion

12. Explain how CO2 is able to control fire.



  1. SO2 and NO2 cause pollution by increasing a) alkalinity  b) acidity  c) buffer solution  d) none
  2. To control electrical fire which of the following is used and give reasons? a) sand  b) water  c) solid carbon tetrachloride  d) Fomite
  3. On placing an inverted tumbler over a burning candle, the flame extinguishes after some time. This is because on non availability of: a) oxygen  b) water vapors  c) carbon di oxide  d)wax
  4. If a person’s clothes catches fire, the best way to extinguish the fire is to: a) throw water on the clothes  b) use fire extinguisher  c) cover the person with a woolen blanket
  5. In fractioning column, various techniques are obtained at various heights of the column. As the vapor reach at height where temperature is equal to or just below the boiling point of that fraction, it will:  a) condense to form a liquid  b) remain in gaseous state  c) condense to form a solid  d) escape from the column
  6. Which cannot control fire due to oils and give reasons: a) fire extinguisher  b) fomite  c) sand  d) water
  7. Burning coal in closed room produces carbon mono oxide. Give reasons.
  8. Why do fire extinguisher cans don’t keep water in them and why does fire brigade uses water to douse fire? Give reasons to explain both the situations.
  9. In oil wells, X forms the topmost layer, followed by Y and finally Z, so X, Y and Z are respectively   a) natural gas, oil and water   b) Petroleum gas, oil and natural gas  c) natural gas, water and oil  d) Petroleum gas, oil and water
  10. How is acid rain caused? Why is it harmful to living organisms?
  11. Why does the portion of copper wire brought near the outside of the burning flame turn red hot?
  12. Why are flames produced when burning some substance like kerosene oil or molten wax and only heat is produced when charcoal is burnt?


  1. Read the following statements carefully:  X: It is a fossil fuel used in thermal power plants to produce electricity    Y: It is a porous black and almost pure form of carbon    Z: It is a mixture of about 200 substances   X,Y and Z are respectively :   a) Petroleum, coal gas, coke  b) Coal, coke , cng gas c) CNG, Bitumen, diesel  d) Coal gas, petrol, paraffin wax
  2. Read the statements and select the correct options: Statement 1: Phosphorus burns in air at room temperature  Statement 2: It is an example of spontaneous combustion  a) Both statements 1 and 2 are true and statement 2 is correct explanation of statement 1  b) Both statements 1 and 2 are true but statement 2 is not correct explanation of 1  c) Statement 1 is true and statement 2 is false  d) Both statements 1 and 2 are false
  3. Read the statements and select the correct options: Statement 1: Kerosene oil and wood do not catch fire on their own temperature. Statement 2: A combustible material cannot catch fire as long as its temperature is lower than its ignition temperature. a) Both statements 1 and 2 are true and statements 2 is correct explanation of statement 1   b) Both statements 1 and 2 are true but statement 2 is not the correct explanation of statement 1  c) Statement 1 is true and statement 2 is false  d) Both statement 1 and 2 are false
  4. Read the statements and select the correct options: Statement1: Amount of heat energy produced on complete combustion of 1kg of fuel is called calorific value. Statement 2: The lower the calorific value of the fuel, will mean that lower combustion is taking place in the fuel. a) Both statements 1 and 2 are true and statements 2 is correct explanation of statement 1   b) Both statements 1 and 2 are true but statement 2 is not the correct explanation of statement 1  c) Statement 1 is true and statement 2 is false  d) Both statement 1 and 2 are false
  5. Choose the correct statement about inflammable substances from the following. They have: a) low ignition temperature and cannot catch fire easily :  a) High ignition temperature and can catch fire easily  b) Low ignition temperature and can catch fire easily   c) High ignition temperature and cannot catch fire easily.
  6. Boojho did the following experiment: He took 2 burning candle (a short and a long candle) and stuck in on the base of a bowl. He then poured some vinegar in the bowl and then slowly added baking soda. He found that the short candle extinguished first and the long candle flickered. Can you think a of an argument as to why did it happen.
  7. It is difficult to burn a heap of green leaves but dry leaves catch fire immediately. Give reasons.
  8. How do you think deforestation is adding to the cause of global warming. Explain with a valid reason.


  1. Global warming and combustion are inter related. Explain how.
  2. Research shows acid rain is one of the causes of cancer in urban areas. Can you think of a valid reason on how it affects the human body. ( clue: acids and bases)