Question: how many grams of hydrogen are present in three moles of hydrogen gas?
Answer: As hydrogen gas is diatomic, 3 moles of hydrogen gas contains 3 x 6.022 x 10^23 H2 molecules, each containing 2 hydrogen atoms. Therefore, 3 moles of hydrogen gas contains 2 x 3 x 6.022 x 10^23 hydrogen atoms, or 3.6132 x 10^24.