Sulphide ores of metals are usually concentrated by forth floation proces. Which one of the following sulphide ores offers an exception and is conventrated by chemical leaching'

Options

A. Argentite
B. Galena
C. Copper pyrite
D. Sphalerite

Explanation

To solve the question regarding which sulfide ore is concentrated by chemical leaching instead of the froth flotation process, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Froth Flotation Process**:
- Froth flotation is a method used to separate hydrophobic materials from hydrophilic ones. It is commonly used for the concentration of sulfide ores.

2. **Identifying Sulfide Ores**:
- Sulfide ores include various metal sulfides such as galena (lead sulfide, PbS), chalcopyrite (copper iron sulfide, CuFeS2), and sphalerite (zinc sulfide, ZnS).

3. **Recognizing Exceptions**:
- While most sulfide ores are concentrated using froth flotation, some sulfide ores can be concentrated using chemical leaching.

4. **Chemical Leaching Process**:
- Chemical leaching involves dissolving the metal from the ore using a chemical solution. A common method for silver sulfide ores is the cyanide process.

5. **Specific Example - Argentite**:
- Argentite (Ag2S) is a silver sulfide ore that is concentrated using the cyanide process. In this process, argentite is treated with sodium cyanide (NaCN) in the presence of oxygen and water, forming a soluble complex (NaAg(CN)2) and sodium sulfide (Na2S).

6. **Conclusion**:
- Based on the information, argentite is the sulfide ore that is an exception and is concentrated by chemical leaching rather than froth flotation.

### Final Answer:
The sulfide ore that is concentrated by chemical leaching instead of the froth flotation process is **argentite (Ag2S)**.