Question

An element has a body centred cubic structure with edge cell of 288 pm .The density of the element is 7.2 g/cm3.How many atoms are present in 208g of the element.

Answer 1

You must first determine the atomic mass of the element.
Convert 288 pm to cm then
volume = (?cm)^3 = volume unit cell
mass unit cell is volume x density = ?
Substitute for mass unit cell = [(#atoms/unit cell) x atomic mass/6.02E23] and solve for atomic mass of element.

Then moles element = 208/atomic mass.
mols x 6.02E23 = # atoms.
Post your work if you get stuck.