Answer
The total charge of all the electrons present is $-4.6\times10^8C$. The net charge is 0.
Work Step by Step
First find out how many moles of gold there are in 12 kg, multiply by the number of atoms per mole and then by the number of electrons in an atom to find the total number of electrons. Then, multiply by the charge per electron.
$$Q=(12kg)\frac{1mole Au}{0.197kg}\frac{6.022\times10^{23}atoms}{mole}\frac{79e^-}{atom}\frac{-1.602\times10^{-19}C}{e^-}$$
$$=-4.6\times10^8C$$
The net charge of the bar is 0. The charge of all the protons cancels out the charge of all the electrons.