Potassium chloride crystallizes with the rock salt structure. When bathed in X-rays, the layers of atoms corresponding to the surfaces of the unit cell produce a diffracted beam of X-rays (¥ë=154 pm) at an angle of 6.97¨¬. From this, the density can be calculated and is ____ g/cm3.
Rock salt structure is cubic. The X-ray diffraction angle and the Bragg angle formula will tell you the separation of the layers. That equals the side length of a unit cube.
From that information and the molecular weight, you can derive the density.
It would be easier to measure directly, it seems to me.