(a) Calculate the packing efficiency in c ccp crystal lattice.
(b) What is the number of particles per unit cell of a simple cube.

Explanation

(a) Let a is the edge length of the cube,
Each unit cell in hcp (or) ccp has effectively 4 spheres. Total volume of fous sphere is equal to `4 xx (4)/(3) pi r^(3)` and volume of the cube is `a^(3) or (2 sqrt(2) ar)^(3)`
Packing efficiency of ccp `= ("Volume occupied by 4 spheres in the unit cell")/("Total volume of the unit cell" (a^(3)))`
`= (4 xx (4)/(3) pi r^(3) xx 100)/((2 sqrt(2) r)^(3)) = 74%`
(b) 1 or one.