Sulphuric (sulfuric) acid is a diprotic acid. When one mole of molecules dissolve in water, two moles of ions would be produced.
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On the other hand, sodium hydroxide is a monoprotic base. When one mole of formula units dissolve in water, only one mole of hydroxide ions would be produced.
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Note that and react at a one-to-one ratio:
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As a result, it would take of to react with the of that was released when of is dissolved in water. Since one mole of formula units could produce only one mole of , it would take of formula units to produce that of for reacting with of .