Multiply the number of mole of hydrogen by the ratio to get to the number of mole of ammonia molecules
2/3 X 3 =2 moles
No
you must calculate the number of ammonia molecules
No
you must start with mass. You are given the mass of hydrogen (6g)
You have 6 grams of hydrogen.
Convert the mass into moles of hydrogen by dividing by the formula
mass of a hydrogen molecule(2 atomic mass units)
Stoichiometry exercise


Ammonia is formed when nitrogen gas reacts with hydrogen gas according to the equation on the right. If 6 grams of hydrogen gas reacts completely, what number of ammonia molecules will be formed? Do you need help? If Yes click once on the equation on the right to display the help diagram. Click twice to hide the help diagram. Click on the squares in the help diagram for more information. 
