Given,

We know the dimension and density of its unit cell.

Let,

The edge length of a unit cell = a

The volume of the cell = a³

Density = d

Atomic mass = M

Mass of unit cell = No. of atoms in unit cell x Mass of each atom = Z × m

Mass of an atom present in the unit cell, m = M/ N_a

where N_a is the Avogadro’s number.

We know, d = Mass of unit cell / Volume of unit cell = Zm/a³ = Z.M /a³N_a

Therefore, Atomic mass, M =( da³N_a) / Z