If the resistivity of copper is $1.7\times {10}^{-6}\mathrm{\Omega }$ cm, then the mobility of electrons in copper, if each atom of copper contributes one free electron for conduction, is [The atomic weight of copper is 63.54 and its density is 8.96 g/cc]:

Mobility of electron $\mathrm{\mu }=\frac{\mathrm{\sigma }}{\mathrm{ne}}-\left(1\right)$
also resistivity $\mathrm{\rho }=\frac{1}{\mathrm{\sigma }}$
From Eqs. (i) and (ii) , we get $\mathrm{\mu }=\frac{1}{\mathrm{ne\rho }}$
Here, n = number of free electrons per unit volume 
$\begin{array}{l}\mathrm{n}=\frac{{\mathrm{N}}_0\times \mathrm{d}}{ \mathrm{atomic} \mathrm{weight} }\\ \mathrm{n}=\frac{6.023\times {10}^{23}\times 8.96}{63.54}=8.5\times {10}^{22}\end{array}$
From Eqs. (iii) and (iv) , we get 
$\begin{array}{l}\mathrm{\mu }=\frac{1}{8.5\times {10}^{22}\times 1.6\times {10}^{-19}\times 1.7\times {10}^{-6}}\\ \therefore \mathrm{\mu }=43.25{\mathrm{cm}}^2/\mathrm{Vs}\end{array}$