Which of the following is a primary cell?

Primary cells are those in which the cell reaction occurs only once and the cell becomes dead after some time. They cannot be recharged or reused.

Dry cell (Leclanche cell) and Mercury cell are examples of primary cells.

Lead storage battery and Nickel-Cadmium (Ni-Cd) cell are secondary cells, which can be recharged by passing current through them in the opposite direction.

Fuel cells are galvanic cells that convert the energy of combustion of fuels directly into electrical energy, requiring a continuous supply of reactants.

Therefore, the dry cell is a primary cell.

Answer: Dry cell