How does NaCN act as a depressant in preventing ZnS from forming the froth ?

Explanation

### Step-by-Step Solution:

1. **Understanding the Froth Flotation Process**:
- Froth flotation is a method used for separating hydrophobic materials from hydrophilic ones. It is commonly used in the extraction of sulfide ores, where the desired metal is separated from its ore.

2. **Identifying the Ores**:
- In this case, we are dealing with two sulfide ores: Galena (PbS) and Sphalerite (ZnS). Both ores can be present together, and we need to separate lead from zinc.

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