Use Avogadro's number to figure out the particle count. The molar mass of iron is roughly 55.85 g/mol. Thus, 0.215 moles would be equivalent to 12 grams of iron. Avogadro's number of particles, approximately 6.022 x 10^23, is included in one mole. So 12 grams of iron contain about 1.3 x 10^23 particles.
