6.3 ADDITIONAL QUESTIONS:
1. Name the most common fuel used in homes.
Ans. Liquefied Petroleum Gas. (LPG)
2. Name the most common fire extinguisher.
Ans. Water
3. What are the states in which a fuel may exist?
Ans. A fuel may exist in solid, liquid or gaseous state.
4. Name any two combustible substances.
Ans. Charcoal, wood
5. Does magnesium produce heat and light during its combustion?
Ans. Yes, it does.
6. What acts as a fuel for our body.
Ans. Food
7. Give two examples of non-combustible substances.
Ans. Water, sand
8. How are heat and light produced in the sun?
Ans. In the sun, heat and light are produced by nuclear reactions.
9. Where were matchsticks first used?
Ans. Egypt
10. What are the three essential requirements for combustion?
Ans. Fuel, air (to supply oxygen) and heat (to raise the temperature of the fuel beyond the ignition temperature) .
11. What is the ignition temperature of phosphorus?
Ans. 25°C
12. What is the colour of an LPG flame?
Ans. Blue
13. What type of process is combustion?
Ans. A chemical process
14. Name an ideal fuel.
Ans. Compressed Natural Gas (CNG)
15. What is the composition of the head of a matchstick?
Ans. Antimony trisulphide and Potassium chlorate.
16. Which part of a flame does a goldsmith blow for melting gold and silver?
Ans. The goldsmith blows the outermost zone of a flame for melting gold and silver.
17. What is the unit for expressing the calorific value of a fuel?
Ans. Kilojoules per kilogram (kJ/kg)
18. Comparing the calorific values of coal and petrol, state which fuel is better.
Ans. The calorific value of coal is about 25,000 – 33,000 kJ/kg, whereas that of petrol is 45,000 kJ/kg. Hence, petrol is a better fuel.
19. What is deforestation?
Ans. The cutting down of trees on a large scale is termed as deforestation.
20. Give any two examples of carbon fuels.
Ans. Coal, petroleum
21. What does magnesium burn to form?
Ans. Magnesium burns to form magnesium oxide and produces heat and light
22. What does coal produce during its combustion?
Ans. Coal produces carbon dioxide, heat and light during its combustion.
23. What is combustion?
Ans. Combustion is a chemical process in which a substance reacts with oxygen to give off heat.
24. Define ignition temperature of a fuel.
Ans. The lowest temperature at which a fuel catches fire is called its ignition temperature.
25. How does a matchstick catch fire?
Ans. By rubbing a matchstick against a rough surface (friction), it attains its ignition temperature and thus catches fire.
26. Why is sodium kept immersed in kerosene?
Ans. Sodium has very low ignition temperature, i.e., it catches fire on coming in contact with air, so it is kept in kerosene.
27. What are combustible and non-combustible substances.
Ans. Substances which undergo combustion are said to be combustible, whereas non-combustible substances are those which don’t burn.
28. What are inflammable substances. Give examples.
Ans. The substances which have very low ignition temperature and can easily catch fire with a flame are called inflammable substances; e.g., LPG, petrol, alcohol, etc.