During electrolytic refining of copper, the anode contains $\mathrm{Cu}$ with $\mathrm{Zn}$, $\mathrm{Ag}$ and $\mathrm{Au}$ impurities. Given $E^{\circ }(\mathrm{Zn}{}^{2+}/\mathrm{Zn})=-0.76\mathrm{V}$, $E^{\circ }(\mathrm{Cu}{}^{2+}/\mathrm{Cu})=+0.34\mathrm{V}$, $E^{\circ }(\mathrm{Ag}{}^{+}/\mathrm{Ag})=+0.80\mathrm{V}$, $E^{\circ }(\mathrm{Au}{}^{3+}/\mathrm{Au})=+1.50\mathrm{V}$, and that the cell is run at a small voltage so that only copper is deposited at the cathode, which statements are correct?

1. A$\mathrm{Zn}$ is oxidised at the anode and stays in solution as $\mathrm{Zn}{}^{2+}$
2. B$\mathrm{Zn}{}^{2+}$ is reduced at the cathode along with $\mathrm{Cu}{}^{2+}$
3. C$\mathrm{Ag}$ and $\mathrm{Au}$ are not oxidised and settle as anode mud
4. DThe concentration of $\mathrm{Cu}{}^{2+}$ in the electrolyte falls slowly while that of $\mathrm{Zn}{}^{2+}$ rises