What is the function of a salt bridge?

The standard reduction potential data at $25^{\circ} C$ is given below.
$E^{\circ}(Fe^{3+}, Fe^{2+}) = +0.77 \ V$
$E^{\circ}(Fe^{2+}, Fe) = -0.44 \ V$
$E^{\circ}(Cu^{2+}, Cu) = +0.34 \ V$
$E^{\circ}(Cu^{+}, Cu) = +0.52 \ V$
$E^{\circ}(O_{2(g)} + 4H^{+} + 4e^{-} \rightarrow 2H_{2}O) = +1.23 \ V$
$E^{\circ}(O_{2(g)} + 2H_{2}O + 4e^{-} \rightarrow 4OH^{-}) = +0.40 \ V$
$E^{\circ}(Cr^{3+}, Cr) = -0.74 \ V$
$E^{\circ}(Cr^{2+}, Cr) = -0.91 \ V$
Match $E^{\circ}$ of the redox pair in List-$I$ with the values given in List-$II$ and select the correct answer using the code given below the lists:

List-$I$	List-$II$
$P. \ E^{\circ}(Fe^{3+}, Fe)$	$1. \ -0.18 \ V$
$Q. \ E^{\circ}(4H_{2}O \rightleftharpoons 4H^{+} + 4OH^{-})$	$2. \ -0.4 \ V$
$R. \ E^{\circ}(Cu^{2+} + Cu \rightarrow 2Cu^{+})$	$3. \ -0.04 \ V$
$S. \ E^{\circ}(Cr^{3+}, Cr^{2+})$	$4. \ -0.83 \ V$

Codes: $P \quad Q \quad R \quad S$

Efficiency of a cell with cell reaction under standard conditions is $70\%$. Cell reaction:
$A_{(s)} + B^{\oplus} \longrightarrow A^{\oplus} + B_{(s)}$ ; $\Delta H^o = -551.5 \ kJ$. Calculate standard electrode potential of cell (in $volt$).

Which of the following will not displace hydrogen from dilute acids?

Identify the overall oxidation reaction that occurs in a lead storage cell during discharge.

Consider the galvanic cell: $A_{(s)} | A_{(aq)}^{+2} || B_{(aq)}^{+} | B_{(s)}$. If the $EMF$ of the cell is positive,identify the correct cell reaction from the following.