Largest safe voltaic cell voltage from electrode potential differences

Steps:

• Identify anode (left electrode) and cathode (right electrode) in each cell notation for spontaneous reaction.
• Use standard reduction potentials: Cu²⁺/Cu (+0.34 V), Zn²⁺/Zn (-0.76 V), Mg²⁺/Mg (-2.37 V), Na⁺/Na (-2.71 V).
• Calculate E°_cell = E°_cathode - E°_anode for each viable cell.
• Evaluate safety for school lab use, avoiding highly reactive metals.

Why D is correct:

• E°_cell = +0.34 V - (-2.37 V) = 2.71 V, the largest voltage per the Nernst equation for standard conditions, with Mg safer than alkali metals.

Why the others are wrong:

• A: E°_cell = -0.76 V - (+0.34 V) = -1.10 V (non-spontaneous; reverse yields only 1.10 V, less than D).
• B: Both electrodes in ZnSO₄(aq) creates no potential difference (E°_cell ≈ 0 V).
• C: Na reacts violently with water in CuSO₄(aq), unsafe for lab despite high E°_cell = +0.34 V - (-2.71 V) = 3.05 V.

Final answer: D