Why a mercury cell gives a constant voltage throughout its life ?

Explanation

**Step-by-Step Solution:**

1. **Understanding the Mercury Cell**: A mercury cell is a type of electrochemical cell that uses mercury and zinc as its primary components. It is known for providing a stable voltage output.

2. **Overall Reaction in the Mercury Cell**: The chemical reaction occurring in a mercury cell can be represented as:
\[ \text{Zn (s)} + \text{Hg}_2\text{O (s)} \rightarrow \text{ZnO (s)} + \text{Hg (l)} \]
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