Which among the following reactions will take place spontaneously?

Calculate the $emf$ of the cell $Cu_{(s)} | Cu^{2+}_{(aq)} || Ag^+_{(aq)} | Ag_{(s)}$. Given: $E^0_{Cu^{2+}/Cu} = +0.34 \ V$,$E^0_{Ag^+/Ag} = +0.80 \ V$.

Assertion : Copper reacts with $HCl$ and liberates hydrogen.
Reason : Hydrogen is present above $Cu$ in the reactivity series.

What is the standard reduction potential $(E^o)$ for $Fe^{3+} \to Fe$ ? ............... $V$
Given that :
$Fe^{2+} + 2e^- \to Fe;$ $E^o_{Fe^{2+}/Fe} = -0.47 \ V$
$Fe^{3+} + e^- \to Fe^{2+};$ $E^o_{Fe^{3+}/Fe^{2+}} = +0.77 \ V$

The $E^{\circ}$ values of half-cells are given below. Which combination of two half-cells will result in a cell with the maximum potential?
$(i) \, A^{3-} \rightarrow A^{2-} + e^{-}; E^{\circ} = 1.5 \, V$
$(ii) \, B^{+} + e^{-} \rightarrow B; E^{\circ} = 0.5 \, V$
$(iii) \, C^{2+} + e^{-} \rightarrow C^{+}; E^{\circ} = 0.5 \, V$
$(iv) \, D \rightarrow D^{2+} + 2e^{-}; E^{\circ} = -1.15 \, V$

Standard electrode potential for $Sn^{4+}/Sn^{2+}$ couple is $+0.15 \ V$ and that for the $Cr^{3+}/Cr$ couple is $-0.74 \ V.$ These two couples in their standard state are connected to make a cell. The cell potential will be ........ $V$