When does a cell reaction occur spontaneously?

Electrode potential of the half cell $Hg(\ell) | Hg_2Cl_{2(s)} | Cl^-_{(aq)}$ can be increased by

Four alkali metals $A$,$B$,$C$ and $D$ have standard electrode potentials of $-3.05 \ V$,$-1.66 \ V$,$-0.40 \ V$ and $0.80 \ V$ respectively. Which one will be the most reactive?

If $E^{\circ}(Fe^{+2}_{(aq)} \mid Fe_{(s)}) = -0.44 \ V$ and $E^{\circ}(Sn^{+2}_{(aq)} \mid Sn_{(s)}) = -0.14 \ V$,what is the standard $emf$ of the cell containing the two electrodes?

Standard electrode potentials are given:
$A^{+}/A = -2.93 \ V$ $B^{+}/B = 0.80 \ V$
$C^{2+}/C = -2.37 \ V$ $D^{3+}/D = -0.74 \ V$
Increasing order of reducing power of these metals:

The $E^0_{cell}$ of the cell $Al(s)|Al^{3+}(1M)||Pb^{2+}(1M)|Pb(s)$ is $1.5 \text{ V}$. If $E^0_{Pb^{2+}/Pb}$ is $-0.14 \text{ V}$, then the standard electrode potential $E^0_{Al^{3+}/Al}$ will be: (in $\text{ V}$)