In order to determine the mole ratio, we need to begin with a balanced chemical equation. For this reaction the balanced chemical equation is 2 H 2 + O 2 → 2 H 2 O The mole ratios are determined using the coefficients of the substances in the balanced chemical equation. 2 m o l H 2 : 1 m o l O 2 : 2 m o l H 2 O The mole ratio for O 2 H 2 O is: 2 m o l H 2 : 1 m o l O 2 2 m o l H 2 1 m o l O 2 or 1 m o l O 2 2 m o l H 2 1 m o l O 2 : 2 m o l H 2 O 1 m o l O 2 2 m o l H 2 O or 2 m o l H 2 O 1 m o l O 2 I hope this was helpful.