Sodium metal crystallizes In body centered cubic lattice with the cell edge, a= 4.29 A.What is the radius of sodium atom? (III-.JEE 1994)

A metal crystallizes into two cubic phases, face centered cubic (fcc) and body centered cubic (bcc), whose unit cell lengths are 3.5 A° and 3.0 A°, rcspcctively. Calculate the ratio of densities of fcc and bcc. (IIT-JEE 1999)

The ratio of the densities of fcc to bcc is

A metallic element crystallizes into a lattice containing a sequence of layers ABABAB....Any packing of spheres leaves out voids in the lattice. What percentage by volume of this lattice is empty space? ( IIT-.IEF 2006)

The sequence ABABAB... indicates hcp unit cell. Now, there are 6 atoms per unit cell and volume of the umt cell is 24√2 r3.Thus, the packing fraction is: