The reaction between sodium hydroxide (NaOH) and phosphoric acid (H₃PO₄) can produce three different salts, depending on the ratio of reactants:

1. Sodium dihydrogen phosphate (NaH₂PO₄)

* Reaction: NaOH + H₃PO₄ → NaH₂PO₄ + H₂O

* This is formed when one mole of NaOH reacts with one mole of H₃PO₄.

* It is a monobasic salt (one acidic hydrogen atom remains).

2. Disodium hydrogen phosphate (Na₂HPO₄)

* Reaction: 2NaOH + H₃PO₄ → Na₂HPO₄ + 2H₂O

* This is formed when two moles of NaOH react with one mole of H₃PO₄.

* It is a dibasic salt (two acidic hydrogen atoms remain).

3. Trisodium phosphate (Na₃PO₄)

* Reaction: 3NaOH + H₃PO₄ → Na₃PO₄ + 3H₂O

* This is formed when three moles of NaOH react with one mole of H₃PO₄.

* It is a tribasic salt (all three acidic hydrogen atoms are replaced by sodium).

The formation of each salt is driven by the neutralization of the acidic hydrogen atoms in phosphoric acid by the hydroxide ions from sodium hydroxide.