Four half reactions I to IV are shown below:

I. $$2 \mathrm{Cl}^{-} \rightarrow \mathrm{Cl}_2+2 \mathrm{e}^{-}$$

II. $$4 \mathrm{OH}^{-} \rightarrow \mathrm{O}_2+2 \mathrm{H}_2 \mathrm{O}+2 \mathrm{e}^{-}$$

III. $$\mathrm{Na}^{+}+\mathrm{e}^{-} \rightarrow \mathrm{Na}$$

IV. $$2 \mathrm{H}^{+}+2 \mathrm{e}^{-} \rightarrow \mathrm{H}_2$$

Which two of these reactions are most likely to occur when concentrated brine is electrolysed?

Which of the following cell was used in Apollo space programme?