The combining ratio of NaOH (sodium hydroxide) to H2SO4 (sulfuric acid) can be determined from the balanced chemical equation for their reaction. In a neutralization reaction between sodium hydroxide and sulfuric acid, the balanced chemical equation is as follows:
2NaOH + H2SO4 -> Na2SO4 + 2H2O
From this equation, you can see that 2 moles of sodium hydroxide (NaOH) react with 1 mole of sulfuric acid (H2SO4) to produce 1 mole of sodium sulfate (Na2SO4) and 2 moles of water (H2O).
So, the combining ratio of NaOH to H2SO4 is 2:1. For every 2 moles of NaOH, you need 1 mole of H2SO4 to fully react in this neutralization reaction.