Which of the following is not used to construct a salt bridge?

Which of the following formulae is used to obtain the value of $E_{\text{cell}}^{\circ}$ for a reaction taking place in a Dry cell?

What is an electrode and a half-cell? Explain their symbolic representation with a suitable example.

In a $Cu-Zn$ electrochemical cell:

For a hydrogen-oxygen fuel cell at $1 \text{ atm}$ and $298 \text{ K}$, the reaction is $H_{2(g)} + \frac{1}{2} O_{2(g)} \rightarrow H_{2}O_{(l)}$; $\Delta G^{\circ} = -240 \text{ kJ}$. The $E^{\circ}$ for the cell is approximately (Given $F = 96,500 \text{ C}$): (in $\text{ V}$)

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 ........ $V$.