Question

The density of solid Cr is 7.15 g/cm3. How many atoms are present per cubic centimeter of Cr?

Answer 1

in one cubic centimetre there are 7.15 g of Cr .. since the density is that.

find the number of moles since you know the mass (and you can find the molar mass of a periodic table):

moles=mass/molar mass

then multiply the number of moles by avogadros number (6.023x10^23) to find the amount of particles (in your case atoms)

# of atoms = moles x avogadros number