of the elements whose properties
those of metals and nonmetals?
12. Write the full form of LED.
13. Name the metal which is usually electroplated on car parts
bicycle handlebars made of steel.
14. Name the fuel which is used in jet aircraft engines.
15. Name the product of coal which is thick black liquid having
# Each of the following scary 2 marks (2x 5 =10)
16. Which material is called black gold and why?
17. Explain why distilled water does not conduct electricity but
electricity?
18. Define malleability and ductility.
19. Can you store lemon pickle in aluminium utensils ? Explain
20. Why is it dangerous to touch a working electrical appliance
# Each of the followings carry 3 marks ( 3x5 =15)
Answers
Answer:
12. Light emitting diodes
13. chromium
14. kerosene
15. coal tar
16. Many useful substances are obtained from petroleum and natural gas. These are termed as ‘petrochemicals’. These are used in the manufacture of detergents, fibres, polythene and other man-made plastics. Hydrogen gas obtained from natural gas, is used in the production of fertilizers. Due to its great commercial importance, petroleum is also called‘black gold’.
17. When salt is dissolved in distilled water, we obtain salt solution. This is a conductor of electricity.
The water that we get from sources such as taps, hand pumps, wells and ponds is not pure. It may contain several salts dissolved in it. Small amounts of mineral salts are naturally present in it. This water is thus a good conductor of electricity. On the other hand, distilled water is free of salts and is a poor conductor.
18. The property of metals by which they can be beaten into thin sheets is called malleability.
The property of metal by which it can be drawn into thin wires is called ductility.
19. No, we cannot store lemon pickle in aluminium utensils,as metals react with acids to liberate hydrogen gas. The pickle can be spoiled.
20. It is dangerous to touch an working electrical appliances because the electricity flow into them.
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