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

Density of fcc=`(Z_(1)xx "At. Mass")/("Av. No." xx V_(1))`
and density in bcc=`(Z_(2)xx"At. Mass")/("Av. No." xx V_(2))`
`(d_("fcc"))/(d_("bcc"))=(Z_(1))/(Z_(2))xx(V_(2))/(V_(1))`
For fcc `Z_(1)=4, V_(1)=a^(3)=(3.5xx10^(-8))^(3)`
For fcc `Z_(2)=2, V_(2)=a^(3)=(3.0xx10^(-8))^(3)`
`(d_("fcc"))/(d_("bcc"))=(4xx(3.0xx10^(-8))^(3))/(2xx(3.5xx10^(-8))^(3))=1.259`