In the reaction #2H_2O -> 2H_2 + O_2#, if you start with 2 mol of water, how many moles of hydrogen gas are produced?
You would end up with 2 moles of Hydrogen gas.
This is a fairly simple example of a titration. We use titrations to calculate how many (grams, moles, litres, molecules, etc.) of one compound/element we would have if we are given a specific amount(grams, moles, litres, molecules, etc.) of another compound/element. To do a titration you must have a balanced equation.
The equation for this example looks like this:
You use the coefficients (big numbers in front of a compound/element in the balanced equation) to get the numbers for the equation. In this question the coefficient 2 in front of
Essentially what you are doing in this equation is taking the number the equation gives you and converting it to moles through unit conversion. This example was already in moles so we skipped that. Then you do another unit conversion from moles of your original compound to moles of the compound you want(using the relationship between the compounds found in the balanced equation; 2=2)
I hope this helps!