Which statement about the hydrogen-oxygen fuel cell is NOT correct?

AThe reactants are supplied continuously from outside
BThe only product of the cell reaction is water
CLike a dry cell, it stores a fixed amount of chemical energy inside the cell
DIts efficiency is much higher than that of a thermal power plant

Answer: C

A fuel cell converts the chemical energy of a fuel fed continuously from outside into electricity; it does not store energy itself and keeps working as long as

H X_{2}

and

O X_{2}

are supplied. The cell reaction

2 H X_{2} + O X_{2} 2 H X_{2} O

gives only water, and the efficiency is about 70% against roughly 40% for a thermal plant. Statement (C) is wrong.

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