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Explain the following.

a. Why is the tungsten used almost exclusively for filament of electric lamps?
 
Tungsten is commonly used as a filament in electric bulbs because of its properties. Those are
 
(i) It has .
 
(ii) It has a .
 
(iii) It is not easily .

b. Why are the conductors of electric heating devices, such as bread-toasters and electric irons, made of an alloy rather than a pure metal?
 
The conductors of electric heating devices are made of alloys rather than a pure metal because it has ,  and are not easily .
 
 and  is preferred as a heating element in electrical appliances such as bread-toasters and electric irons.