What forms at each electrode?

You will write functions that decide what forms at the cathode and at the anode when a salt solution is electrolysed between platinum electrodes. You will also find the least voltage that starts the electrolysis.

The idea. At the cathode the couple with the higher potential is reduced, and water competes at $-0.83\ \text{V}$. At the anode the couple with the lower potential is oxidised, and water competes at $1.60\ \text{V}$.

Your tasks.

1. Complete cathode_product(cation) so that it returns "metal" when the cation is reduced before water, and "H2" when water is.
2. Complete anode_product(anion) so that it returns "anion" when the anion is oxidised before water, and "O2" when water is.
3. Complete least_voltage(cation, anion) so that it returns the potential of the couple oxidised minus the potential of the couple reduced, in volts.