Here's how to determine the net ionic equation for the reaction between phosphoric acid (H₃PO₄) and sodium hydroxide (NaOH):

1. Write the balanced molecular equation:

H₃PO₄(aq) + 3NaOH(aq) → Na₃PO₄(aq) + 3H₂O(l)

2. Write the complete ionic equation:

3H⁺(aq) + PO₄³⁻(aq) + 3Na⁺(aq) + 3OH⁻(aq) → 3Na⁺(aq) + PO₄³⁻(aq) + 3H₂O(l)

3. Identify and cancel out the spectator ions:

Spectator ions are the ions that appear on both sides of the equation and do not participate in the reaction. In this case, Na⁺ and PO₄³⁻ are spectator ions.

4. Write the net ionic equation:

3H⁺(aq) + 3OH⁻(aq) → 3H₂O(l)

Simplified Net Ionic Equation:

H⁺(aq) + OH⁻(aq) → H₂O(l)

This net ionic equation represents the essential reaction occurring between phosphoric acid and sodium hydroxide, which is the formation of water from hydrogen ions and hydroxide ions.