The reaction between Hydrogen and Oxygen under normal conditions is characterized by the following balanced equation:
2 H₂ + O₂ → 2 H₂O
The mole ratio (based on the coefficient used to balance the chemical equation) of H₂ : O₂ is 2 : 1.
Thus there are two times as many moles of H₂ in the reaction as there are moles of O₂.
∴ if the moles of H₂ = 1.75 mol
then the moles of O₂ = 1.75 mol ÷ 2
= 0.875 mol
Now, Mass = Moles × Molar Mass
Thus the mass of oxygen gas = 0.875 mol × 32 g/mol = 28 g
Thus the answer is 28 grams.