A metal crystallises into two cubic phases , face centred cubic (fcc) and body centred cubic (bcc) , whose unit cell lengths are 3.5 Å and 3.0 Å , respectively. The ratio of densities of fcc and bcc is

Explanation

Density `prop (N)/(a^(3))`
`rArr " " (d_(1))/(d_(2)) = (N_(1))/(N_(2)) ((a_(2))/(a_(1)))^(3) = (4)/(2) ((3)/(3.5))^(3) = 1.26`