KF has NaCl structure. If distance between `K^(+)` & `F^(-)` is 269 pm, find the density of KF. (At mass of K = 39 and F = 19).

Explanation

To find the density of KF given the distance between \( K^+ \) and \( F^- \) is 269 pm, we can follow these steps:

### Step 1: Determine the Edge Length (a)
The distance between \( K^+ \) and \( F^- \) is given as 269 pm. In the NaCl structure, the relationship between the edge length \( a \) and the ionic radii \( R^+ \) (for \( K^+ \)) and \( R^- \) (for \( F^- \)) can be expressed as:
\[ a = 2(R^+ + R^-) \]
Assuming \( R^+ \) is the radius of \( K^+ \) and \( R^- \) is the radius of \( F^- \), we can denote:
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