`NH_(4)^(+)and Br^(-) " ions"` have ionic radii of 143 pm and 196pm respectively. The coordination number of `NH_(4)^(+) "ion in" NH_(4)Br` is

Explanation

To determine the coordination number of the \( NH_4^+ \) ion in \( NH_4Br \), we can follow these steps:

### Step 1: Identify the ionic radii
We are given the ionic radii of the ions:
- Radius of \( NH_4^+ \) = 143 pm
- Radius of \( Br^- \) = 196 pm

### Step 2: Calculate the radius ratio
The radius ratio is calculated using the formula:
\[ \text{Radius Ratio} = \frac{\text{Radius of cation}}{\text{Radius of anion}} \]
Substituting the values:
\[ \text{Radius Ratio} = \frac{143 \, \text{pm}}{196 \, \text{pm}} \approx 0.730 \]

### Step 3: Determine the coordination number using the radius ratio
According to the radius ratio rules:
- If the radius ratio is between 0.225 and 0.414, the coordination number is 4 (tetrahedral void).
- If the radius ratio is between 0.414 and 0.732, the coordination number is 6 (octahedral void).
- If the radius ratio is greater than 0.732, the coordination number is typically 8.

Since our calculated radius ratio of approximately 0.730 falls within the range of 0.414 to 0.732, we conclude that the coordination number is 6.

### Final Answer
The coordination number of \( NH_4^+ \) ion in \( NH_4Br \) is **6**.

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