Question: how many atoms are there in 10g of carbon?
Answer: 1 mole of carbon-12 has 6.02 x 1023 atoms. Second, you need to know how many moles there are in 20 grams of carbon-12. One mole of anything is the same number of grams as the molecular mass. Since the molecular mass of carbon-12 is 12, there are 12 grams in 1 mole of it, and therefore 20/12 = 5/3 moles in 20 grams.