Why the graphite rods in the extraction of aluminium from molten `Al_2 O_3` have to be replaced from time to time ?

Explanation

To answer the question of why the graphite rods in the extraction of aluminium from molten Al2O3 have to be replaced from time to time, we can break down the explanation into several key points:

### Step-by-Step Solution:

1. **Understanding the Process**: The extraction of aluminium from molten Al2O3 is carried out using the Hall-Héroult process, which is an electrolytic method. In this process, an electrolytic cell is used where aluminium oxide (Al2O3) is dissolved in molten cryolite (Na3AlF6) to lower the melting point and increase conductivity.

**Hint**: Familiarize yourself with the Hall-Héroult process and its components, including the electrolytic cell and the materials used.

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