In `ZnS` (zinc blende) strucutre, the `CN` of each ion ie `4`.

Explanation

To determine the coordination number (CN) of each ion in the zinc sulfide (ZnS) structure, specifically in the zinc blende structure, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Structure**:
ZnS crystallizes in the zinc blende structure, which is a face-centered cubic (FCC) lattice. In this structure, zinc ions (Zn²⁺) and sulfide ions (S²⁻) alternate in occupying the tetrahedral voids.

**Hint**: Recall the basic structure of zinc blende and its arrangement of ions.

2. **Identify the Coordination Number**:
The coordination number of an ion in a crystal structure refers to the number of nearest neighbor ions surrounding it. In the case of tetrahedral coordination, each ion is surrounded by four other ions.

**Hint**: Remember that tetrahedral voids are surrounded by four spheres.

3. **Determine the Coordination Number for Zn²⁺**:
In the zinc blende structure, Zn²⁺ ions occupy alternate tetrahedral voids. Each Zn²⁺ ion is coordinated to four S²⁻ ions.

**Hint**: Visualize the tetrahedral arrangement of the ions around Zn²⁺.

4. **Determine the Coordination Number for S²⁻**:
The S²⁻ ions form a face-centered cubic lattice. In this arrangement, each S²⁻ ion is also surrounded by four Zn²⁺ ions, leading to a coordination number of 4 for S²⁻ as well.

**Hint**: Consider how the FCC structure allows for the coordination of surrounding ions.

5. **Conclusion**:
Therefore, in the zinc blende structure of ZnS, both Zn²⁺ and S²⁻ ions have a coordination number of 4.

**Final Answer**: The coordination number (CN) of each ion (Zn²⁺ and S²⁻) in ZnS (zinc blende) structure is 4.