Which of the above has the lowest thermal conductivity? a) Copper. c) Iron. b) Aerated brick. d) Vacuum e) Air

Vacuum has the lowest thermal conductivity.
This can be confirmed by the coefficient of thermal conductivity of the material:
clay porous brick = 0.26 W / (m * C)
copper = 386.9 W / (m * C)
iron = 74.4 W / (m * C)
air = 0.025 W / (m * C)
vacuum = 0 W / (m * C)

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