Which chemical works as reducing agent in the process of poling ?

Explanation

### Step-by-Step Solution:

1. **Understanding Poling**: Poling is a metallurgical process used for the purification of metals, particularly copper. It is a method that helps in removing impurities from metal ores.

2. **Identifying the Impurities**: In the case of copper, the common impurity is copper oxide (Cu2O). Similarly, for tin, the impurity can be tin oxide (SnO2).

3. **Role of Reducing Agents**: A reducing agent is a substance that donates electrons in a chemical reaction, thereby reducing another substance. In the context of poling, a reducing agent is needed to convert metal oxides into pure metals.

...