Hydrochloric acid: HCl(aq)
Sodium hydroxide: NaOH(aq)
The two substances react in an acid-base neutralization reaction to produce aqueous sodium chloride and liquid water.
The complete ionic equation is:
H⁺(aq) + Cl⁻(aq) + Na⁺(aq) + OH⁻(aq) → Na⁺(aq) + Cl⁻(aq) + H₂O(l).