What is the function of a salt bridge in a Daniell cell?

In the electrochemical cell $H_{2(g)}, 1 \ atm \ | \ H^+_{(aq)}, 1 \ M \ || \ Cu^{2+}_{(aq)}, 1 \ M \ | \ Cu_{(s)}$,which of the following statements is true?

Given $\lambda^{\circ}_{Mg^{2+}} = 106 \ S \ cm^2 \ mole^{-1}$ and $\lambda^{\circ}_{SO_4^{2-}} = 160 \ S \ cm^2 \ mole^{-1}$. The value of $\lambda^{\circ}_{MgSO_4}$ (in $S \ cm^2 \ mole^{-1}$) is

Write the cell reaction of a lead storage battery when it is discharged. How does the density of the electrolyte change when the battery is discharged?

The Gibbs energy for the decomposition of $Al_2O_3$ at $500^oC$ is as follows:
$\frac{2}{3} Al_2O_3 \rightarrow \frac{4}{3} Al + O_2$
$\Delta_rG = +960 \ kJ \ mol^{-1}$
The potential difference needed for the electrolytic reduction of aluminium oxide $(Al_2O_3)$ at $500^oC$ is at least ........ $V$.

What is the approximate standard free energy change per mole of $Zn$ (in $kJ \ mol^{-1}$) for a Daniell cell at $298 \ K$?