Write down the basic assumptions of the Drude model.

$BCC$ iron with lattice parameter a $=0\mathrm{.}2866nm$ has electrical conductivity $=9\mathrm{.}71{10}^{-1}m$ at room temperature. Using a free electron model and assuming three valence electrons per atom, calculate: $($i$)$ the concentration of conduction electrons, and $($ii$)$ the relaxation time,

Given that $m=9\mathrm{.}11{10}^{-31}kg,$ and $e=1\mathrm{.}6{10}^{-19}C.$