Answer
Fraction lost $=2.4\times10^{-10}=2.4\times10^{-8}\%$.
Work Step by Step
First find the total charge of all the electrons in the copper.
$$Q=(3.0g)\frac{1mole Cu}{63.5g}\frac{6.022\times10^{23}atoms}{mole}\frac{29e^-}{atom}\frac{-1.602\times10^{-19}C}{e^-}$$
$$=1.32\times10^5C$$
Now calculate the fraction lost.
Fraction lost = $\frac{32\times10^{-6}C}{1.32\times10^5C }=2.4\times10^{-10}=2.4\times10^{-8}\%$.
