What is the total number of atoms per unit cell in a face-centred cubic (fcc) crystal structures ?

Answer

56

Explanation

`(72.36)/(56) 'Fe' (27.64)/(16) 'O' rArr 1.292 'Fe', 1.7275 ' O'`
Hence proportion is `1 : 1.33`, so Empirical formula is `Fe_(3) O_(4)`, Empirical formula mass = 232 amu Now if there are x formula units in the unit cell
`5.2 = ((x(232))/(6.02 xx 10^(23)))/((8.39 xx 10^(-8))^(3)) rArr x = 7.9688`
Hence number of ion in the unit cell = 56