A colourless gas is produced on heating strongly a piece of black clectrode used in dry cell. This gas turns lime water milky, of what material is the electrode made?

Explanation

To determine the material of the black electrode used in a dry cell, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Colorless Gas**:
- The problem states that a colorless gas is produced when a black electrode is heated strongly.
- We need to identify this gas based on its reaction with lime water.

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