a metal crystallizes into two cubic phases,fcc and bcc.whose unit cell lengths are 4.0 and 3.0 angstroms respectively.the ratio of densities of fcc and bcc is

Hi,

Use the eqn

$ = ZM/(a³ N_a)

$ = density

z = rank (no. of atoms per unit cell)

a = unit cell length

N_a = Avogadro number

$₁/$₂ = z₁ a₂³ / z₂ a₁³

         = 4 * 3³ / 2 * 4³

          = 27 / 32

because there are 4 atoms in fcc and 2 atoms in bcc

Thanks

Anurag