For the cell Zn(s)|Zn2+(aq)\|Mx+(aq)|M(s), different half cells and their standard electrode potentials are given…

Strategy: The question asks for the maximum value of $E^\circ_{\text{cell}}$ per electron transferred. This is defined as $(E^\circ_{\text{cathode}} - E^\circ_{\text{anode}}) / n$, where $n$ is the number of electrons in the reduction half-reaction.

Step 1: Setup calculations for all half-cells Anode is Zinc: $E^\circ_{\text{anode}} = -0.76\text{ V}$. Formula: $\text{Value} = \frac{E^\circ_{\text{cathode}} - (-0.76)}{n}$

1. $\ce{Au^{3+}/Au}$: $\frac{1.40 + 0.76}{3} = \frac{2.16}{3} = 0.72$
2. $\ce{Ag^+/Ag}$: $\frac{0.80 + 0.76}{1} = 1.56$ (Maximum)
3. $\ce{Fe^{3+}/Fe^{2+}}$: $\frac{0.77 + 0.76}{1} = 1.53$
4. $\ce{Fe^{2+}/Fe}$: $\frac{-0.44 + 0.76}{2} = 0.16$

Step 2: Conclusion The silver electrode gives the highest potential per electron.

$\boxed{\text{Answer: (a) } \ce{Ag^+/Ag}}$