e) (i) Select the species which is the strongest reducing agent? (ii) Write a cell diagram for the cell obtained by coupling A and B.

• A: $\text{Fe}^{3+} (\text{aq}) + \text{e}^- \rightleftharpoons \text{Fe}^{2+} (\text{aq})$ $E^\circ = +0.77 \text{ V}$
• B: $\text{Cr}_2\text{O}_7^{2-} (\text{aq}) + 14\text{H}^+ (\text{aq}) + 6\text{e}^- \rightleftharpoons 2\text{Cr}^{3+} (\text{aq}) + 7\text{H}_2\text{O}$ $E^\circ = +1.33 \text{ V}$
• C: $\text{Cl}_2 (\text{g}) + 2\text{e}^- \rightleftharpoons 2\text{Cl}^- (\text{aq})$ $E^\circ = +1.6 \text{ V}$

A reducing agent is a species that gets oxidized (loses electrons). In a table of standard reduction potentials, the strongest reducing agents are the products of the half-reactions with the lowest (most negative) standard reduction potentials.
Comparing the $E^\circ$ values: $+0.77 \text{ V}$ (A), $+1.33 \text{ V}$ (B), and $+1.6 \text{ V}$ (C), the lowest potential is $+0.77 \text{ V}$ for half-reaction A.
The reducing agent in half-reaction A is $\text{Fe}^{2+} (\text{aq})$.

The strongest reducing agent is $\boxed{\text{Fe}^{2+} (\text{aq})}$.

e) (ii) Write a cell diagram for the cell obtained by coupling A and B.

When coupling two half-cells, the one with the lower standard reduction potential will undergo oxidation (anode), and the one with the higher standard reduction potential will undergo reduction (cathode).

• Half-cell A: $E^\circ = +0.77 \text{ V}$
• Half-cell B: $E^\circ = +1.33 \text{ V}$ Since $E^\circ (\text{A}) < E^\circ (\text{B})$, half-cell A will be the anode (oxidation) and half-cell B will be the cathode (reduction).

• Anode (oxidation): $\text{Fe}^{2+} (\text{aq}) \rightarrow \text{Fe}^{3+} (\text{aq}) + \text{e}^-$
• Cathode (reduction): $\text{Cr}_2\text{O}_7^{2-} (\text{aq}) + 14\text{H}^+ (\text{aq}) + 6\text{e}^- \rightarrow 2\text{Cr}^{3+} (\text{aq}) + 7\text{H}_2\text{O}$

The general convention for a cell diagram is: $\text{Anode} | \text{Anode solution} || \text{Cathode solution} | \text{Cathode}$.
For half-cells involving only ions in solution, an inert electrode (like Platinum