Four voltaic cells are set up. In each, one half-cell contains a standard hydrogen electrode. The second half-cell is one of the following:
(i) Cr³⁺(aq, 1.0 M) | Cr(s)
(ii) Fe²⁺(aq, 1.0 M) | Fe(s)
(iii) Cu²⁺(aq, 1.0 M) | Cu(s)
(iv) Mg²⁺(aq, 1.0 M) | Mg(s)
(a) In which of the voltaic cells does the hydrogen electrode serve as the cathode?
(b) Which voltaic cell produces the highest potential? Which produces the lowest potential?