Zn + 2HCl → ZnCl2 + H2 How many moles of hydrogen are produced from the reaction of three moles of zinc with an excess of hydrochloric acid?
Would it not be THREE MOLES with respect to dihydrogen?
We follow the stoichiometry...
And if 6 mol of the acid are added to 3 mol of the metal...THREE moles of dihydrogen gas should result.
How do you know that hydrogen gas is bimolecular, i.e. diatomic? In fact all of the elemental gases, well all of the ones with any chemistry, are diatomic, i.e.
What is the mass of your quantity of dihydrogen gas?