Predict the structure of MgO crystal and the co-ordination number of the cation in which the radii of the cation and anion are 65 pm and 140 pm respectively.

Explanation

To predict the structure of the MgO crystal and the coordination number of the cation, we can follow these steps:

### Step 1: Identify the given data
- Radius of cation (Mg²⁺): 65 pm
- Radius of anion (O²⁻): 140 pm

### Step 2: Calculate the radius ratio
The radius ratio (r+) is calculated using the formula:
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