Question

We know that free electrons in the metals make metals good conductor of electricity, what is the cause for good thermal conductivity of metals in general? which metal is the poorest conductor of heat?

Answer 1

Thermal conductivity of metal arises from electrons. Where as in non metals, thermal conductivity arises from the lattice vibration. In metal ration of thermal conductivity to electrical conductivity is proportional to absolute temperature (Wiedemann–Franz law)
Thermal conductivity of polonium is 0.2 W/(mK)