In which form is `ZnO` subjected to smelting in retords made of clay ?

Explanation

To answer the question regarding the form in which ZnO is subjected to smelting in retorts made of clay, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Ore**: Zinc is primarily extracted from its ore, which is zinc sulfide (ZnS), commonly known as zinc blend.

2. **Roasting Process**: The first step in the extraction process is roasting, where zinc sulfide (ZnS) is heated in the presence of oxygen. This reaction produces zinc oxide (ZnO) and sulfur dioxide (SO2):
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