Answer: 6 moles
Explanation:
The balanced equation for this reaction is [tex]2\text{H}_{2}+\text{O}_{2} \longrightarrow 2\text{H}_{2}\text{O}[/tex].
This means that for every 2 moles of water produced, 2 moles of hydrogen are consumed.
Thus, if 6 moles of water are produced, this means 6 moles of hydrogen are consumed.