Which of the following is a secondary (rechargeable) cell?

A secondary cell can be recharged by passing current in the reverse direction, because the discharge products stay on the electrodes and can be converted back. The Ni-Cd cell ($\mathrm{Cd}+2\mathrm{Ni}(\mathrm{OH}){}_3\to \mathrm{CdO}+2\mathrm{Ni}(\mathrm{OH}){}_2+\mathrm{H}{}_2\mathrm{O}$) is such a cell, as is the lead storage battery. The dry cell and mercury cell are primary cells, and a fuel cell is neither; it is fed with reactants continuously.