Question

Which of the following is not used as cooking utensils even being a metal?
A.Copper
B.Lead
C.Silver
D.Iron

Answer 1

Hint:Any metal which is to be used for cooking purposes should be a good conductor of heat. Though metals are considered to be good conductors, some of them still are poor conductors because of absence of free conducting electrons.

Complete answer:
First let us see what thermal conductivity is. Thermal conductivity is the ability of a material to conduct or transfer heat from one point to another. The opposite of thermal conductivity is thermal resistivity. Materials having good thermal conductivity are used in heat sinks whereas materials having good thermal resistivity are used as thermal insulators.
A metal can be considered a good thermal conductor if it has free electrons. According to Wiedemann-Franz law, thermal conductivity is proportional to product of absolute temperature and the electronic conductivity. When temperature increases, the thermal conductivity of a pure metal decreases.
The metals given here are all pure metals. Copper is a good conductor of electricity so it is also a good conductor of heat. Silver is also a good conductor of electricity so it is a good conductor of heat. Iron is also known to be a good conductor of heat. Lead on the other hand is the weakest heat conductor among the given metals.

So, option B is the correct answer.

Note:
Apart from lead, steel is also a poor conductor of heat because it is an alloy and lacks free electrons. Aluminum conducts heat at the fastest rate with an average of 14 seconds. Due to strong covalent bonding and low phonon scattering, diamond is a good conductor of heat.