Consider the crystal structure of sodium chloride which is modeled as a set of touching spheres. Each sodium atom has a radius and each chlorine atom has a radius r. The centres of the spheres from a simple cubic lattice. The packing fraction of this system is 27 + (c)t +r (d) * " 2, +)
Packing fraction is defined as the ratio of volume of atoms occupying the unit cell to the volume of unit cell...this is the formula of packing fraction. you can easily calculate.....