A metal has a fcc lattice. The edge length of the unit cell is 404 pm. The density of the metal is 2.72g cm–3. The molar mass of the metal is (N_A Avogadro constant = 6.02 × 10²³mol^-1) 

d=2.72gcm⁻³ density of crystal

z = no. of effective constituent particles in one unit cell

M = Molecular weight

a=404pm edgelength of unit cell

N_A​=6.022×10²³

Density of cubic unit cell-

$\mathrm{d} =\frac{\mathrm{ZM}}{{\mathrm{N}}_0{\mathrm{a}}^3}$

For an FCC, Z=4

M=$\frac{{\mathrm{dN}}_{\mathrm{A}}{\mathrm{a}}^3}{\mathrm{Z}}$

M =$\frac{2.72\times {(404\times {10}^{-10})}^3\times 6.023\times {10}^{23}}{4}$
=27g/m