Question -
Answer -
By knowing the density of an unknown metal andthe dimension of its unit cell, the atomic mass of the metal can be determined.
Let ‘a’ be the edge length of a unitcell of a crystal, ‘d’ be the density of the metal, ‘m’ bethe mass of one atom of the metal and ‘z’ be the number ofatoms in the unit cell.
Now, density of the unitcell
[Since mass of the unit cell = Number ofatoms in the unit cell × mass of one atom]
[Volume of the unit cell = (Edge length of thecubic unit cell)3]
From equation (i), we have:
Now, mass of one atom of metal (m) 
Therefore,
If the edge lengths are different(say a, b and c), then equation (ii)becomes:
M = d(abc)NAz (iv)M = d(abc)NAz (iv)
From equations (iii) and (iv), wecan determine the atomic mass of the unknown metal.