Question: how many atoms are there in one gram of hydrogen?
Answer: Because the molecular mass of Hydrogen is 1gram/mole, there is 1 mole of hydrogen in 1 gram of hydrogen atoms. For every mole, there are 6.02*10^23 atoms so in 1 gram of hydrogen there are 6.02*10^23 hydrogen atoms (in scientific notation) this is equal to 602000000000000000000000 hydrogen atoms.