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 unit cell `(rho)=(ZxxM)/(N_(0)xxa^(3))`
Density of f.c.c. unit cell = `(4xxM)/(N_(0)xx(3.5Å)^(3))`
Density of b.c.c. unit cell `=(2xxM)/(N_(0)xx(3.0Å)^(3))`
`("Density of f.c.c")/("Density of b.c.c")=(4xxM)/(N_(0)xx(3.5Å)^(3))xx(N_(0)xx(3.0Å)^(3))/(2xxM)=(108)/(85.75)=1.259`