$(a)$ Give reasons why tungsten is used for making the filament of electric lamps.
$(b)$ Why are the heating elements of electrical appliances made up of an alloy rather than a pure metal?

(N/A) Tungsten is used for making the filament of electric lamps because:
$(i)$ It has a very high melting point (approximately $3380^{\circ}C$),which allows it to glow at high temperatures without melting.
$(ii)$ It has high resistivity,which allows it to produce a large amount of heat when current passes through it.
$(b)$ Heating elements are made of alloys because:
$(i)$ Alloys have higher resistivity than pure metals,which generates more heat.
$(ii)$ Alloys do not oxidize (burn) easily even at high temperatures,which increases the longevity of the appliance.