Identify the reactants and products in the molecular equation: HI(aq) + NaOH(aq) → NaI(aq) + H₂O(l).
Write the complete ionic equation by dissociating all strong electrolytes into their respective ions: HI(aq) dissociates into H⁺(aq) and I⁻(aq), NaOH(aq) dissociates into Na⁺(aq) and OH⁻(aq), and NaI(aq) dissociates into Na⁺(aq) and I⁻(aq).
The complete ionic equation is: H⁺(aq) + I⁻(aq) + Na⁺(aq) + OH⁻(aq) → Na⁺(aq) + I⁻(aq) + H₂O(l).
Identify and cancel out the spectator ions, which are ions that appear on both sides of the equation without undergoing any change. In this case, Na⁺(aq) and I⁻(aq) are spectator ions.
Write the net ionic equation by removing the spectator ions: H⁺(aq) + OH⁻(aq) → H₂O(l).