Answer:
3.925 mol.
Explanation:
2 Na₂O₂(s) + 2 H₂O(l) → 4 NaOH(s) + O₂(g) ,
It is clear that 2 moles of Naâ‚‚Oâ‚‚ react with 2 moles of Hâ‚‚O to produce 4 moles of NaOH and 1 mole of Oâ‚‚ .
Using cross multiplication:
4 moles of NaOH produced with → 1 mole of O₂ .
15.7 moles of NaOH produced with → ??? mole of O₂ .
∴ The no. of moles of O₂ made = (1 mole)(15.7 mole)/(4 mole) =  3.925 mol.