For a redox reaction,$Oxi + ne^- \rightarrow Red$,what is the correct form of the Nernst equation?

For the electrochemical cell shown below:
$Pt \mid H_{2}(p=1 \, atm) \mid H^{+}(aq., x \, M) \mid\mid Cu^{2+}(aq., 1.0 \, M) \mid Cu_{(s)}$
The potential is $0.49 \, V$ at $298 \, K$. The $pH$ of the solution is closest to:
[Given: Standard reduction potential,$E^{\circ}$ for $Cu^{2+}/Cu$ is $0.34 \, V$; Gas constant,$R = 8.31 \, J \, K^{-1} \, mol^{-1}$; Faraday constant,$F = 9.65 \times 10^{4} \, J \, V^{-1} \, mol^{-1}$]

To find the standard potential of $M^{3+}/M$ electrode,the following cell is constituted:
$Pt | M | M^{3+} (0.001 \ mol \ L^{-1}) || Ag^{+} (0.01 \ mol \ L^{-1}) | Ag$
The $emf$ of the cell is found to be $0.421 \ V$ at $298 \ K$. The standard potential of the half-reaction $M^{3+} + 3e^{-} \to M$ at $298 \ K$ will be .............. $V$.
(Given $E^{o}_{Ag^{+}/Ag}$ at $298 \ K = 0.80 \ V$)

What is the oxidation potential of $0.05 \, M \, H_2SO_4$ in volts?

Determine the electrode potential of $Sn^{2+}(0.01 \text{ M}) | Sn(s)$ at $25^{\circ} \text{C}$ if $E^0_{Sn^{2+}/Sn}$ is $-0.136 \text{ V}$. (in $\text{ V}$)

If $E^{\circ}_{\text{cell}}$ for $Cd_{(s)} | Cd_{(1M)}^{2+} || Ag_{(1M)}^{+} | Ag_{(s)}$ is $1.2 \ V$,what is the emf of the cell at $25^{\circ} C$ (in $V$)?