Lead–acid batteries are heavy. Much lighter rechargeable cells are nickel–cadmium batteries used in electronic equipment.

Other than their chemical composition, discuss two major differences between fuel cells and nickel–cadmium cells.

fuel cells produce only water / Cd and Ni are toxic (heavy metals);

fuel cells are more expensive;

fuel cells can operate continuously/do not need recharging;

fuel cells are more unwieldy/less portable/less self-contained/need supply of \({{\text{O}}_{\text{2}}}\) and \({{\text{H}}_{\text{2}}}\);

Accept opposite statements for NiCd cells.

Part (c) was better answered, with most able to gain at least one of the four possible scoring points.