Number of atom in 1 g of copper,

$\mathrm{n}=\frac{\mathrm{Avogadro}\mathrm{number}}{\mathrm{Atomic}\mathrm{weight}}=\frac{6.02\times {10}^{23}}{63.5}=9.48\times {10}^{21}$

Therefore, number of atoms i.,e, number of free electrons in l mg of copper,

$\mathrm{n}\text{'}=9.48\times {10}^{21}\times {10}^{-3} =9.48\times {10}^{18}$

Charge possessed by these free electrons,
$\mathrm{q}= \mathrm{n}\text{'}\mathrm{e}= 9.48\times {10}^{18}\times 1.6\times {10}^{-19}= 1.517\mathrm{C}$