How many grams of water could be made from 5.0 mol #H_2# and 3.0 mol #O_2#?
We need a stoichiometric equation as our starting point.....
The stoichiometric equation unequivocally tells me that
We have a
And so ONLY
This is something worth spending time on if you don't see it immediately. This is an example of stoichiometric equivalence, where a MASS of reagent, dihydrogen, dioxygen, etc. REPRESENTS a NUMBER of dihydrogen, dioxygen molecules, which is what a molar quantity is. If you have another query.......ask.