KF has ccp structure. Calculate the radius of unit cell if the side of the cube is 400 pm. How many F

ions Octrahedral voids are there in this unit cell

For ccp structure, edge length, a = 2 $\sqrt{2 } r$
Hence, radius r = a/2$\sqrt{2}$ = 400/​2$\sqrt{2}$ = 282.84 pm
​Now, we knwo that,
In CCP structure, 
Contribution of atoms on corners = 1/8 x 8 = 1
Contribution of atoms at faces = 1/2 x 6 = 3
So, no. of total atoms(N) = 1+3 = 4
Now, the octahedral voids = N and 
Tetrahedral voids = 2N
So, here 4 Fluroide ions are in octahedral voids.