How many moles of H2O are produced when 25.6 grams of oxygen are used?

1.6 moles H2O

Explanation: The chemical reaction in the formation of water is:

2 H2 + O2 => 2 H2O

Find first the number of moles of O2

25.6 g O2 x 1mole O2 / 32 g O2 = 0.8 moles O2

Do the mole ratio:

0.8 moles O2 x 2 moles H2O / 1 mole O2 = 1.6 moles H2O