Question

Thermal conductivity of aluminium, copper and stainless steel increasing in the order
A. Copper > aluminium >stainless steel
B. Stainless steel > copper >aluminium
C. Aluminium > copper > stainless steel
D. Copper > stainless steel > aluminium

Answer 1

Hint:We can define the thermal conductivity in simple words that the rate of heat transferred by conduction through a unit cross-sectional area of material.
Higher thermal conductivity means the material is a good conductor of heat and it can transfer heat faster.

Complete step by step solution:
The thermal conductivity of a material is a measure of its ability to conduct heat
In solid thermal conductivity defined with the help of a free electron model there are a number of free electrons present in solids. These electrons are not bound to any molecule of metal they can freely move within the metal. When one end of a metal is heated, then the average kinetic energy of the free electron at that end increases. And start vibrating with large amounts of amplitude and give some energy to their neighbouring free electrons by colliding with them .these free electrons repeat the same process with other neighbouring electrons and free them to move with high vibrations this process heat transferred in solids.

Thus the transition of heat energy in metals takes place by free electrons, not by molecules.

From this we can observe that the higher no of free electron metal have higher heat conductivity

The approximate value of thermal conductivity of metal witch given in question are written below-

Copper	401 Wm${}^{-1}$K${}^{-1}$
Aluminium	237 Wm${}^{-1}$K${}^{-1}$
Stainless steel	20 Wm${}^{-1}$K${}^{-1}$

From this we can arrange these metals as
Copper > aluminium > stainless steel

So here option A is correct

Note:It is clear that the reason for the high thermal conductivity of metals is that the number of free electrons is present. This is why in metals the transmission of heat takes place very rapidly. Bad conductors have hardly any free electrons. Hence heat conduction in them takes place very slowly.