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Statement
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Status
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Reason
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(A) It converts energy of combustion into electrical energy
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Incorrect
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This describes a Fuel Cell (like the $\text{H}_2\text{-}\text{O}_2$ fuel cell), which converts the chemical energy of a fuel ($\text{H}_2$) and an oxidant ($\text{O}_2$) into electrical energy. The mercury cell converts stored chemical energy into electrical energy.
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(B) It is rechargeable
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Incorrect
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The mercury cell is a Primary Cell, meaning the chemical reactions are irreversible. It is designed for single-use and cannot be recharged.
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(C) The cell reaction involved is $\text{Zn}(\text{Hg})+\text{HgO}(\text{s})\to\text{ZnO}(\text{s})+\text{Hg}(\text{l})$
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Correct
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This is the overall, net reaction for the mercury cell (or zinc-mercuric oxide cell). It shows the oxidation of the Zinc amalgam ($\text{Zn}(\text{Hg})$) and the reduction of Mercuric oxide ($\text{HgO}$).
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(D) It is a low current device used in hearing aids
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Correct
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Mercury cells are typically small, button-shaped batteries designed for low-current devices like watches, calculators, and hearing aids. They are valued for their constant voltage output (approximately $1.35 \text{ V}$) over a long period.
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