(Na)2 O + H2O--> 2NaOH. All you have to is write the equation and then notice that you have 2 Na on the left. Therefore you apply a 2 towards SOdium hydroxide and notice it balances the equation. 2 Na's. 2 O's. 2 H's on each side.
What Is The Balanced Equation For Sodium Oxide Combines With Water To Form Sodium Hydroxide?