A metal crystallizes into two cubic phases, face-centred cubic and body-centred cubic, which have unit cell lengths `3.5` and `3.0 A`, respectively. Calculate the ration of densities of fcc and bcc.

Explanation

We know that `d=zM//N_(a)a^(3)`
For fcc, z=4 therefore `d=xxM//Na(3.5xx10^(-8))^(3)g//cm^(3)`
For bcc, z=2 therefore `d.=2xxM//Na(3.0xx10^(-8))^(3)g//cm^(3)`
`d//d.=4(3.5xx10^(-8))^(3)//2(3.0xx10^(-8))^(3)=3.17:1`